OBJECTIVE To determine feasibility and efficacy of concurrent paclitaxel and cisplatin with definitive hyperfractionated radiotherapy (HFRT) in locally advanced head-and-neck squamous cell carcinoma (HNSCC). METHODS Forty-two patients stages III to IV head-and-neck squamous cell carcinoma were enrolled in 2 consecutive prospective trials from August 1998 to January 2006. In study 1, 16 patients received HFRT in 2 courses of 39.6 Gy each with a split of 2 weeks with concurrent paclitaxel (175 mg/m) and cisplatin (100 mg/m) on days 1, 21, 36, and 57. In study 2, 26 patients received a continuous course of 74.4 Gy of HFRT with concurrent weekly paclitaxel (50 mg/m) and cisplatin (30 mg/m). RESULTS Tumor locations included oropharynx 48%, hypopharynx 24%, larynx 12%, paranasal sinuses 7%, salivary gland 2%, oral cavity 2% and unknown primary 5%. In study 1, all patients received 3 to 4 cycles of chemotherapy and completed the programmed radiotherapy course. In study 2, 69% received 5 to 6 cycles of chemotherapy and 92% completed the irradiation. Overall, 93% of objective responses were observed (complete 76%, partial 17%). Median follow-up was 50 months (range: 12-97). Pattern of recurrence was local 8%, distant 13%, and combined 3%. Acute toxicity grades 3 to 4 in studies 1 and 2 was 75% and 88%, respectively (P = ns). Globally, 5-year overall survival were 68%, with a median of 71 months (range: 50-91). On multivariate analysis, male gender (P = 0.04) and complete response (P = 0.01) were predictive of improved survival. CONCLUSIONS HFRT combined with cisplatin and paclitaxel is very active but at the expense of severe toxicity. Efficacy and toxicity in studies.1 and 2 were not different despite completely different treatment strategies (chemotherapy dose intensity vs. radiotherapy dose intensity).