Impaired galactose metabolism has been proposed as a risk factor for ovarian cancer and endometriosis, which is a putative precursor of endometrioid and clear cell histological sub-types of ovarian cancer. The prevalence of the most common galactose-I-phosphate uridyl transferase gene mutations, Q188R and N314D, was assessed in 206 women with ovarian cancer, 78 women with endometriosis and 248 controls. No Q188R mutations were found in any of the groups. A statistically significant increase in the frequency of N314D mutations was observed in women with serous and undifferentiated histological sub-types of ovarian cancer, but not mucinous, endometrioid or clear cell sub-types. There were no significant differences observed in the N314D mutation frequency between women with endometriosis (18%) and controls (17%). Our results support previous reports of an association of impaired galactose metabolism with serous and undifferentiated ovarian cancers but contradict previous findings of increased N314D mutation frequencies among women with endometriosis and endometrioid and clear cell sub-types ovarian cancer.