Does transecting the tendinous insertion of the latissimus dorsi on the humerus improve aesthetic results and avoid the displeasing bulge in the armpit that sometimes occurs when the latissimus dorsi is used for breast reconstruction? In a prospective study, 60 patients who were having breast cancer surgery and simultaneous breast reconstruction using the latissimus dorsi flap were randomized for cutting (n = 29) or leaving intact (n = 31) the tendinous muscle insertion on the humerus. The cosmetic outcome was evaluated by patients and surgeons 6 to 12 months postoperatively. Patients reported good cosmetic results in 29 of 31 cases with the humeral insertion left intact and in 26 of 29 cases when the tendon was cut (p = 0.59), as compared with 21 of 31 cases versus 25 of 29 cases (p = 0.091), according to the surgeon's evaluation. A lateral bulge was more frequently observed by the surgeons in the group with intact insertion (10 of 31 patients), as compared with the group with a transected humeral insertion (2 of 29 patients). Discomfort caused by this bulge was reported by 19 of 31 patients with intact insertion, but only 3 of 29 patients with the tendon cut (p < 0.0001). The additional transection of the tendon was not associated with any complications. The additional transection of the tendinous humeral insertion of the latissimus dorsi muscle improves aesthetic results and avoids a displeasing bulge in the axilla when the latissimus dorsi flap is used for breast reconstruction.