Ovarian cancer and second malignant neoplasms are found to occur rather frequently in the same patient. From a clinical perspective, it is important to have quantitative information on concurrent malignancies in the same year of diagnosis of the epithelial ovarian cancer. In this population-based study, we used data from the Netherlands Nationwide Network for Registry of histo- and cytopathology (PALGA) and the Netherlands Cancer Registry (NCR). Data of the ovarian cancer as well as data on previous or later cancers were obtained. Age-specific cancer rates from the NCR were used to calculate expected numbers of cancer. Between 1987 and 1993, histopathology reports were identified of 4577 patients with primary epithelial malignant or primary borderline malignant ovarian cancers and its longitudinal data. As the database may lack detailed information on histopathology, a recent sample of 789 patients diagnosed with ovarian cancer in 1996-2003 was comprehensively studied as well. In the eventual data analysis of 5366 patients, 244 cases (4.5%) of concurrent primary malignancy were reported in the same year that the malignant epithelial ovarian tumor had been diagnosed against 51 expected. The observed vs expected ratio was 4.8 and the 95% confidence interval (CI) (4.3-5.5). For cancer of the uterus/endometrium the observed vs expected ratio was 62.3 (95% CI 52.5-73.5). For skin, breast, colorectal, urinary bladder, renal and cervical cancer the ratio was also larger than unity. The elevated risk of concurrent cancer may lead to clinical screening protocols. The findings on endometrial cancer may prompt research on common etiologies and biomarkers.