Reproducible subclassification of ovarian carcinomas is biologically and increasingly therapeutically important. The traditional morphologic approach that ignores genotype and immunophenotype is subjective and therefore suboptimal. This review covers the prevalence, morphology, immunophenotype and, in some cases, genotype of each major ovarian cancer subtype. Serous carcinomas, frequently WT1 positive, are morphologically diverse and mimic other tumors. Most transitional cell carcinomas are closely related to them. Mucinous carcinomas are uncommon and should only be diagnosed after extraovarian primaries are excluded; true ovarian mucinous carcinomas are usually low stage. Intestinal and mullerian mucinous (seromucinous) tumors are histogenetically and clinically distinct. Ovarian endometrioid carcinomas almost always resemble endometrioid carcinomas of endometrium, express estrogen receptors (ER) but not WT1, and are frequently low grade and low stage. Ovarian clear cell carcinomas, negative for ER and WT1 and lacking p53 overexpression, have a limited morphologic repertoire and are frequently low stage at presentation. Clinical biology, immunohistochemistry, and genotype can be used to enhance diagnostic objectivity.