Ovary cancer risk in relation to consumption of dairy products was investigated using a self-administered questionnaire on dietary habits and other risk factors for cancer, which was completed in 1986 by 62 573 postmenopausal women participating in the Netherlands Cohort Study. Follow-up for cancer was implemented by annual record linkage with the Netherlands Cancer Registry and a nationwide pathology registry. After 11.3 years of follow-up, data of 252 incident epithelial ovarian cancer cases and 2216 subcohort members were available for analysis. No association was seen between consumption of milk, yoghurt, cheese or fermented dairy products and ovarian cancer risk. The multivariable adjusted relative risk of epithelial ovarian cancer for women in the highest compared to the lowest quintile of intake of lactose or dairy fat was 0.93 (95% confidence interval (CI)=0.60-1.45; P(trend)=0.32) and 1.53 (95% CI=1.00-2.36; P(trend)=0.11), respectively. Lactose or dairy fat intakes were not associated with serous ovarian cancer risk. Our results do not support an association between consumption of dairy products or lactose intake and ovarian cancer.British Journal of Cancer advance online publication, 22 November 2005; doi:10.1038/sj.bjc.6602890 www.bjcancer.com.