The correlation between histological subtype [endodermal sinus (ES), polyvesicular vitelline (PV), glandular (G) and hepatoid (H) subtypes] and the prognosis of pure yolk sac tumours (YSTs) of the ovary was investigated. From 1964 to 1989, 35 patients with YSTs were treated with primary surgery and adjuvant chemotherapy. The prevalence of histological subtypes was as follows: 14 patients had a single subtype, either ES (12) or G (2); 12 patients had two subtypes, ES+G (4), ES+PV (3), ES+H (4) or G+H (1); six patients had three subtypes, ES+P+H (4) or ES+G+H (2); and three patients had all four subtypes. Multivariate analysis showed that important predictors were FIGO stage, chemotherapeutic regimen and residual tumour size. However, for stage I, multivariate analysis showed that the histological subtype was a superior predictor to the subclassification of FIGO stage I, age or chemotherapeutic regimen (P = 0.03). Kaplan-Meier analysis showed that YSTs composed of an admixture of three or four subtypes was associated with a better prognosis than those composed of one or two subtypes (P < 0.01), other variables being constant.