New primary basal cell carcinomas arising in skin flaps following Mohs micrographic surgery for primary and recurrent basal cell carcinoma. Two patients developed new primary basal cell carcinomas (BCCs) in skin flaps used to reconstruct wounds that followed an earlier primary BCC and a recurrent BCC treated by Mohs micrographic surgery. Criteria for distinguishing a new primary BCC arising in a skin flap or full-thickness skin graft at a previous treatment site for BCC from a truly recurrent BCC are presented. The distinction between a new primary BCC and true tumor recurrence is important for accurate clinical assessment and may have a dramatic impact on the type of subsequent treatment. In addition, there may be less medicolegal liability in the case of a new primary BCC arising at the site of a previously treated BCC than for a BCC that is determined to be recurrent. 