Thirty-four ovarian mucinous carcinomas defined by nuclear stratification in excess of three layers (noninvasive mucinous carcinoma, NIMC) or stromal invasion (invasive mucinous carcinoma, IMC) were examined to define prognostic indicators. Twenty-two patients had NIMC (Stage I, 15; Stage II, 1; Stage III, 5; and Stage IV, 1). Twelve patients had IMC (Stage I, one; Stage II, one; and Stage III, ten). Fifteen patients died, ten with IMC and five with NIMC (mean survival, 16.7 months). Nineteen patients survived, two with IMC and 17 with NIMC (mean follow-up, 12 years). Ten of the 12 patients with IMC who died had Stage III disease. Five of the 22 patients with NIMC who died included four with Stage III and one with Stage I disease. Among patients who died, those with IMC tended to have a shorter mean survival than those with NIMC. No differences among groups were identified with respect to nuclear grade, mitotic activity, percentage of tumor displaying more than three cell layers, or amount of invasion. In ovarian mucinous carcinoma, clinical stage and stromal invasion are the most important prognostic variables, and they are interrelated. Stage I NIMC rarely pursues an aggressive course.