Unusual and probably underestimated complications following breast reconstruction with a latissimus dorsi (LD) flap and sub-pectoral implant are the LD muscle twitching and the breast contour deformities from pectoralis major (PM) muscle contraction. Surgical muscle denervation is usually indicated for these complications. Botulinum toxin A (BTX-A) infiltration has been described in reducing breast contour deformity in sub-pectoral implant after breast augmentation or reconstruction. Between January 2002 and April 2006, 71 consecutive patients underwent delayed unilateral breast reconstructions with LD flap and sub-pectoral implant after mastectomy. All patients reporting discomforting signs and symptoms from muscle contraction in the reconstructed breast were included in this prospective study. Thirteen patients (18.3%) were selected and treated with BTX-A percutaneous local injections. Signs and symptoms were evaluated, after 4, 8 and 12 months, by the patients and by a panel of three physicians not involved in the study, using a five-point scale. During the study period all patients reported a decrease or disappearance of the signs and symptoms. After 12 months, 11 patients received three BTX-A infiltrations, demonstrating considerable improvements compared to the pre-treatment status. Wilcoxon matched pairs rank sum test showed a statistical difference between pre-treatment and post-treatment scores after 14 days (P<0.01) and 12 months (P<0.001). Our experience shows that muscular contraction deformities after breast reconstruction with a LD flap plus implant are not uncommon complications. The use of BTX-A infiltrations is an effective, not surgical, low cost and low risk procedure to treat these complications. It is an easy procedure to be performed on an outpatient basis with a temporary effect but safely repeatable and reproducible; it avoids hospitalisation or further surgical procedures and demonstrates tolerable latency with satisfactory outcomes.