There are very few well-designed long-term laser hair removal studies.
Results vary widely and are not accurately predictable at this time.
Some laser hair removal consumers have permanent reduction in the size and color of hairs.
In some consumers, this is a dramatic improvement.
This result is most likely in light-skinned, dark-haired “ideal” candidates.
Even “ideal” candidates do not always respond to treatment.
Despite promotional claims, there is not enough published comparative data to determine if one type of laser targeting melanin is more effective than other types.
Cooling the skin can reduce pain and side effects.
Skin discoloration which can last several months can occur in 1% to 10% of patients, with a higher likelihood in darker skin.
Consumers must avoid sun before and after treatment to reduce the risk of discoloration.
Consumers who have realistic expectations about laser hair removal are often satisfied.
Why clinical data should be given the most weight
Promotional material from manufacturers and practitioners is often unreliable
As noted by pioneering laser researcher Christian Raulin, M.D.: “Laser companies, tattoo and cosmetic studios as well as self-proclaimed “laser institutes” promote their work with full-page advertisements in newspapers and lifestyle magazines… It is not uncommon for the industry to advertise newly developed lasers for which the efficacy has not been determined by means of objective, randomized trials. When a laser is first marketed, there are thus no dependable data available from studies; instead, physicians must rely upon the often unfounded claims from the advertising literature.” 
Personal experiences of consumers are unreliable
While consumer experiences are very important in determining what treatment is like and general satisfaction, it’s very difficult to assess quantitative effectiveness based on one or a few consumers. As I discuss in my section on Vaniqa, one-third of patients using a placebo were judged by physicians to have improvement or even marked improvement, and that was under controlled clinical conditions. There are simply too many variables between individuals to determine if one person’s result will predict your own results.
Consumers are better served when they follow the advice of Whitney Tope, M.D. and Maria Hordinsky, M.D.: “Look for studies incorporating rigorous design to produce believable data and conclusions.” 
Echoing Tope and Hordinsky, laser researcher Sharyn Laughlin recently stated:
“It appears that the laser industry and the clinical arena of epilation are being driven by market forces and economic factors, with a minimum of consideration given to evidence-based medicine. The majority of clinical trials and peer-reviewed reports do not address the issues of permanence or specific dose-response relationships…”
“There are few comparative data to allow physicians and their patients to make rational choices… Patients deserve to know the precise benefits and limitations of the particular system to be used in relation to whether their expectation is for temporary or permanent epilation.” 
Dr. Raulin adds: “Well-founded scientific studies are no longer the basis for the wide-spread use of lasers. Careful clinical assessment cannot occur under such conditions, and the absolute opposite of the Hippocratic Oath to do no damage can easily be achieved.” 
Rox Anderson, M.D., one of the pioneers in the field of laser dermatology agrees “there is a big problem brewing”:
“Unfortunately, there is relatively little good, hypothesis-driven research on lasers in dermatology. These studies are expensive and slow to perform, analyze, present, and publish. The laser companies are quick to promote their new devices and procedures, even before efficacy and safety are well established, and before a specific FDA clearance is given…”
“When poorly researched before use on patients, cosmetic lasers or anything else are no different than the infamous patent medicines of the 19th century… But the problem lies mainly with us, the professionals. We should simply refuse to believe infomercials over peer-reviewed studies… Those industry salesmen who can’t support their claims well, should be tolerated only as village idiots. In short, the patients are ours, and we should make better patient care the only real bottom line.” 
This has been my point since 1995. Luckily, a few researchers have continued to publish rigorous long-term studies.
Published clinical data by type
If you are researching a specific model of laser and don’t know what type it is, ask the practitioner or check this list
Nd:YAG clinical data
Ruby clinical data
Alexandrite clinical data
Diode clinical data
(see also Flash lamp Photoepilator Argon laser)
Raulin C, Greve B, Raulin S. Ethical considerations concerning laser medicine. Lasers in Surgery and Medicine 28:100-101 (2001).
Tope WD, Hordinsky MK. A hair’s breadth closer? Archives of Dermatology. 1998 Jul;134(7):867-9.
Laughlin SA, Dudley DK Long-term Hair removal using a 3-millesecond alexandrite laser. Journal of Cutaneous Medicine and Surgery. 2000 Apr;4(2):83-88.
Anderson RR. Response to "Letter to the Editor.’’ Lasers in Surgery and Medicine 28:102 (2001).
Anderson (1981): A good overview on theories in the optics of human skin and laser interactions.
Anderson (1983): One of the earliest articles about the concept of selective thermolysis, the theory behind laser hair removal.
Wagner (1998): Survey found only 6% of dermatologists thought independent non-physician laser practitioners should be allowed to practice.
Chernoff (1997): A pretty good synopsis of hair physiology, with a very brief discussion on Nd:YAG and ruby lasers.
Bargman (1999): A point-counterpoint article discussing advantages of laser hair removal, with a companion piece on electrolysis (Richards 1999)
Comparative data (hair removal)
Nanni (1998): A practical review for Q-switched Nd:YAG, ruby and alexandrite lasers.
Nanni (1999): A comparison of side effects for Q-switched Nd:YAG, ruby and alexandrite lasers.
Comparative data (other applications)
Rosenbach (1997): A comparison of Q-switched alexandrite and Nd:YAG lasers for nevi removals.