Poor outcome of treatment was found to be associated with low oxygen tension in the primary tumor and not with high intratumor microvessel density in 40 patients with advanced squamous cell carcinoma of the uterine cervix. Multivariate Cox regression analysis identified the total volume of the hypoxic tumor regions, i. e. the tumor subvolume having pO(2) values below 5 mmHg, as a significant prognostic factor for locoregional control, disease-free survival, and overall survival. Other important prognostic factors, identified by univariate Cox regression analysis, were tumor volume, the fraction of pO(2) readings giving pO(2) values below 5 mmHg, and tumor stage.