From 1969 to 1985, 62 patients with squamous cell carcinoma of the oral cavity received preoperative radiotherapy (RT) 40-50 Gy before radical surgery. The time interval between the end of the RT and surgery varied from 4 to 49 days (median 19 days). The cancer specific survival rate was significantly lower for the 32 patients with intervals longer than or equal to 19 days compared with patients with shorter intervals (P = 0.001). The reason for choosing a longer interval between the treatment modalities was not related to stage or performance status, however, a possibility that patients in poor condition were preferentially allocated to the long intertreatment interval group cannot be ruled out. This study suggests that when using combined modalities any effort should be exercised to reduce the time interval between the modalities.