Objective: In several countries the incidence of peritoneal mesotheliomas among women closely mirrors the pattern among men. The aim was to investigate the role of asbestos exposure in the aetiology of peritoneal mesotheliomas in women and men. Methods: All cases of peritoneal mesothelioma were selected from the Swedish and Netherlands Cancer Registers for the period 1989-2003. For both countries incidence rates were calculated and stratified by sex. A linear regression analysis was used to analyse the existence of a trend over time. Results: Among men the incidence rate of peritoneal mesothelioma in the Netherlands (0.60 per 100 000 persons) was consistently higher than in Sweden with an average ratio of 1.8 (range 1.4-2.8). In both countries no trend over time was observed. During the 15-year period in the Netherlands the incidence rate among men was about 3.3-fold higher than among women. In Sweden the incidence rate among women was slightly higher than in men up to 1999, and thereafter about threefold higher among men. This sudden shift was statistically significant and seemed mainly caused by changes in classification of peritoneal tumours. Conclusion: The absence of a time trend in the incidence rate of peritoneal mesothelioma in the Netherlands and Sweden in the past 15 years may point to a more limited role of occupational exposure to asbestos in the aetiology of peritoneal mesothelioma than for pleural mesothelioma, especially among women. The observed drop around 2000 in annual incidence of peritoneal mesothelioma among Swedish women indicates the presence in the past of a substantial misclassification with other tumours in the peritoneum.