Background: Human studies of the short-term cellular effects of tanning salon exposures are lacking. Findings of such studies may prove extremely helpful in educating consumers considering or currently attending tanning salons. Objective: Our purpose was to determine whether tanning salon exposure causes DNA alterations and p53 protein expression in epidermal keratinocytes and/or circulating peripheral lymphocytes. Methods: Eleven subjects received 10 full-body tanning salon exposures over a 2-week period. UV-induced DNA cyclobutane pyrimidine dimers and p53 protein expression were examined, comparing pretreatment peripheral blood lymphocytes and epidermal biopsy specimens with analogous specimens obtained after the 10 tanning salon exposures. Results: Cyclobutane pyrimidine dimers in DNA and p53 protein expression were detected in epidermal keratinocytes, but were absent in lymphocytes. Conclusion: Similar to outdoor sun exposure, short-term recreational tanning salon exposure causes molecular alterations believed essential in the development of skin cancer. (J Am Acad Dermatol 2001;44:775-80.)