INTRODUCTION: The use of vascularised composite free flaps (VCFF) has become a widely accepted method for primary reconstruction of mandibular defects. Adjuvant or neo-adjuvant radiotherapy (RTH) increases susceptibility to trauma and infections. The aim of this study is to compare the incidence of local complications after mandibular reconstruction with vascularised composite free flaps, related to pre- or postoperative radiotherapy. The effects of these complications on functional rehabilitation with a dental prosthesis fixed on bone implants are also studied. METHODS: Between 1990 and 1999, 49 vascularised composite free flaps were used for mandibular reconstructions (41 iliac crest flaps and 8 fibula flaps). 31 patients (63%) underwent preoperative (8) or postoperative (23) radiotherapy. Short (6-12 months) and long-term (over 12 months) outcomes are analysed separately. The incidence of complications depending on the timing of radiotherapy (neo vs adjuvant) was compared. RESULTS: In the first 12 months the complication rates among the irradiated and non-irradiated patients were 26 and 11% respectively. During short-term evaluation complications were seen in 26% of the irradiated patients and 11% of the non-irradiated group. After 12 months the rate of complications rises to 45% for the irradiated and 18% for the non-irradiated patients. 27% of irradiated patients presented with fistula, 27% with exposed metallic plates and 9% developed osteoradionecrosis of the graft. Dental implants were inserted in 29 grafts, among which 9 had secondary radiotherapy. 90% of the non-irradiated patients and 56% of the irradiated patients chewed with the dental prosthesis fixed on bone implants. DISCUSSION: Regardless of pre- or postoperative timing, radiotherapy clearly augments complications, the incidence of which increases with time. Only in one patient did osteoradionecrosis necessitate removal of the dental prostheses. Inability to chew is linked more to the amount of resection of the mobile tongue than to complications of radiotherapy. We therefore recommend systematically placing dental implants during the initial surgery, unless large soft tissue resection preventing adequate swallowing is required.