Objective: To define the percentage of positive sentinel lymph node biopsies and identify risk factors for the presence of lymph node disease in patients with melanomas less than or equal to 1 mm in depth. Design: Retrospective chart review. Setting: Washington University School of Medicine and Barnes-Jewish Hospital, St Louis, Mo, a melanoma referral center with outpatient surgical care. Patients: Forty-six patients with melanomas less than or equal to 1 mm in depth undergoing sentinel lymph node biopsy at our institution between 1996 and 2002. Results: The procedure was well tolerated and there were no reported complications. Of the 46 patients, 3 (7%) (95% exact confidence interval, 1.3%-17.8%) were found to have positive sentinel lymph nodes or micrometastatic disease. The finding of a positive sentinel lymph node was associated with a Clark level of III or more (P≤.07). Conclusions: Conclusions from this study are limited by the small sample size. The results of our study suggest that sentinel lymph node biopsy of patients with melanomas less than or equal to 1 mm in depth may be indicated when the Clark level is III or more.