The purpose of this phase I-II study was to assess the efficacy and toxicity of an accelerated radiation therapy schedule in patients affected with head and neck squamous cell carcinomas of various primary sites. We adopted the concomitant boost technique which allows 1-2 weeks' shorter treatment time by delivering the boost treatment phase as second daily dose during the last part of the basic field irradiation. May 1989 to December 1992, fifty-one patients were scheduled to receive a total dose of 71-75 Gy in 40 fractions over 6 weeks. The boost encompassing the macroscopic disease was given as second daily dose during the last two weeks of the basic treatment. Severe mucositis was observed in 62% of the patients. Late side-effects occurred in 4 patients. At a median follow-up of two years (range: 12-56 months), actuarial locoregional control rate is 44% and overall survival is 54%. At univariate analysis, primary site is the only predictive factor of locoregional control (p = 0.009): neoplasms arising from the oral cavity did worse than those from larynx/hypopharynx and oro/nasopharynx. We conclude that this regimen is feasible in head and neck squamous cell carcinoma of various primary sites. However, since primary site seems to exhibit a predictive value, data from controlled studies are needed to assess its role in primary sites other than oropharynx and nasopharynx.