BACKGROUND: The use of preoperative tumor curettage in Mohs micrographic surgery has never been prospectively systematically assessed. OBJECTIVE: To assess the utility of preoperative tumor curettage in Mohs micrographic surgery for primary or recurrent, well-defined basal cell carcinoma less than 2 cm in diameter located on the head or neck. METHODS: Patients were randomized to either preoperative tumor curettage or control group and were compared in terms of percent surface area increase from tumor surface area to wound surface area, absolute surface area increase, number of tissue layers removed, types of repairs performed, and postoperative complications. Multivariate analysis was performed to see if tumor location, appearance (exophytic or flat), or histology affected any of the above. RESULTS: The preoperative tumor curettage group had a 399% (95% confidence interval [CI] 346-452) mean surface area increase from tumor to wound surface area versus 263% (95% CI 216-311) for control group (P=.0002). The preoperative tumor curettage group had a mean absolute surface area increase of 1.78 cm2 (95% CI 1.57-1.99) versus 1.40 cm2 (95% CI 1.15-1.65) for control group (P=.02). The preoperative tumor curettage group had fewer tissue layers removed (P=.3). Preoperative tumor curettage had no effect on types of repairs performed or number or type of postoperative complications. Tumor appearance and histology had no effect on any of the above end points. CONCLUSION: Preoperative tumor curettage was associated with significantly greater percent surface area increase and absolute surface area increase from tumor surface area to wound surface area. This difference did not affect type of repair performed or postoperative complications.