Periareolar sebaceous cysts at the incision site after mastopexy and reduction mammaplasty are very unpleasant complications that affect the surgical result and the degree of patient satisfaction. The author sought to investigate the cause and prevention of such sebaceous cysts. Sixty patients undergoing mastopexy or reduction mammaplasty were randomly divided into 2 groups. Periareolar de-epithelialization was performed to a depth of superficial layer of the dermis in group A and nearly the full thickness of the dermis in group B, and the incidence of sebaceous cysts was compared between these 2 groups. Patients were followed-up for 2 to 4 years. In group A, sebaceous cysts at the incision site were found in 4 patients (13.3%); however, no sebaceous cysts occurred in group B. Increasing the thickness of de-epithelialization appears to decrease the incidence of sebaceous cysts at the incision site.