Background: There are many circumstances in clinical practice in which it is helpful to have a definitive diagnosis of melanoma before subjecting a patient to mutilating surgery. Previous studies on the effect of incisional biopsy on melanoma prognosis were conflicting and lacked a matched control group to account for the other prognostic indicators. Objective: We set up this study to investigate the effect of incisional biopsy on melanoma prognosis. Methods: The design was of a retrospective case control. Data were obtained from the database of the Scottish Melanoma Group; the database was set up in 1979 to collect detailed clinical, pathologic, and follow-up data on all patients diagnosed with melanoma in Scotland. Each incisional case was matched against 2 excision cases controlling for age, sex, sites, and Breslow thickness. The main outcome measures were time from initial biopsy to recurrence and to melanoma-related death. Results: Two hundred sixty-five patients who had incisional biopsy before definitive excision of melanoma were included in the study; these were matched with 496 cases of excisional biopsy specimens. Cox's proportional hazard model for survival analysis showed that biopsy type had no significant effect on recurrence (P = .30) or melanoma-related death (P = .34). Conclusions: This study is the largest series on the effect of incisional biopsy on melanoma prognosis to date and the first to include matched controls. Melanoma prognosis is not influenced by incisional biopsy,. before definitive excision. (J Am Acad Dermatol 2002;46:690-4.)