The effect of tumor bulk resection on survival was studied in 102 patients with stages II and III ovarian cancer. A multiple linear regression equation provuded both simultenaous control of multiple confounding variables and an assessment of these variables as independent predictors of survival. The most important factors were the histologic grade of the tumor and the size of the largest residual tumor mass after operation. Survival time was uniformly poor if the diameter of the largest residual tumor mass exceeded 1.5 cm irrespective of total tumor volume (mean=12.7 months, SE=1.6 mo). Survival time was inversely proportional to residual mass size under 1.6 cm, and surgery improved survival relative to reduction in mass size below this limit. Extensive resections of tumor bulk with failure to remove all masses greater than 1.5 cm in diameter did not influence survival. Surgery provides optimum benefit when all gross tumor can be excised safely.