Sun exposure is a known cause of melanoma, and there are several reasons for concern that tanning lamp use may also cause melanoma, especially because of the spectral output of the lamps,the similarity of tanning lamp use to natural sun exposure (particularly sunbathing), the reported association of melanoma with PUVA therapy, and the positive results in several case-control studies of melanoma risk and tanning lamp use. We have reviewed the epidemiologic literature relevant to the relation between tanning lamp use and melanoma and have discussed methodologic issues that should be considered in interpreting these reports and designing improved studies. Although several investigations have found a positive relation between tanning lamp use and melanoma, in some instances including dose-response or duration-response effects, the methodologic limitations preclude any firm conclusion regarding a causative relation. Meta-analysis of existing data may provide better information, but several limitations could only be overcome by new studies collecting more precise exposure data. The popularity of tanning lamp use, especially in young persons, adds urgency to the quest for elucidation of the relation between the use of these devices and melanoma risk. (J Am Acad Dermatol 1998;38:89-98.)