AbstractDNA‐ploidy and the percentage of S‐phase cells were measured by DNA flow cytometry in 171 primary squamous cell carcinomas of the head and neck. Of the analyzed tumors, 102 (60%) were aneuploid and 69 (40%) were diploid. Minimum follow‐up was 6 months (median: 37 months). For the whole population no difference of the 5‐year survival rate was found comparing diploid (18%) and aneuploid tumors (26%). Following sequential radiochemotherapy, aneuploid tumors revealed a better 5‐year survival (54%) than diploid tumors (7%;P<0.01). Accordingly, the locoregional control rate was higher for aneuploid tumors (57% vs. 28%; n.s.). By contrast, following surgery and radiotherapy or concurrent radiochemotherapy, diploid and aneuploid tumors had nearly the same survival rates. The analysis of recurrence demonstrated a lower rate of locoregional failures of diploid tumors (surgery + radiotherapy: 32% vs. 44%), but this was leveled out by a higher incidence of distant metastases of diploid carcinomas (surgery + radiotherapy: 36% vs. 17%). Relating to the fraction of S‐phase cells, slowly proliferating tumors (S‐phase