This study attempts to define histologic patterns in 1039 consecutive cases of basal cell carcinoma and to correlate these patterns with adequacy of margins of surgical excision. Five major histologic patterns were identified: nodular, 218 cases (21%); superficial, 181 cases (17%); micronodular, 151 cases (15%); infiltrative, 77 cases (7%); and morpheic, 11 cases (1%). A mixed pattern (two or more major histologic patterns) was present in 401 cases (38.5%). Our study indicates that nodular and superficial basal cell carcinomas can be completely removed by simple surgical excision in a high percentage of cases (93.6% and 96.4%, respectively) whereas the micronodular, infiltrative, and morpheic basal cell carcinomas have a higher incidence of positive tumor margins (18.6%, 26.5%, and 33.3%, respectively) after excision. Mixed patterns that consisted of combinations of the nodular, micronodular, or infiltrative types exhibited a behavior similar to the pattern that resulted in a greater chance of incomplete surgical removal.