Breast ptosis is one of the most common conditions treated by plastic surgeons, but the causes are not clearly defined. A review was conducted of 132 consecutive patients presenting for breast augmentation or mastopexy. Information was obtained by chart review and telephone interview. Standardized photographs were examined to determine degree of ptosis by the Regnault classification. Of patients who had at least one pregnancy, 85% reported adverse changes in breast shape following pregnancy, 35% reported a reduction in breast size, and 30% reported an increase in size. Upon logistic regression, age, history of significant (>50 lbs) weight loss, higher body mass index, larger bra cup size, number of pregnancies, and smoking history were found to be significant risk factors for breast ptosis (P < 0.05). History of breast-feeding, weight gain during pregnancy, and lack of participation in regular upper body exercise were not found to be significant risk factors for ptosis.