Body mass index (BMI) has shown both positive and negative associations with ovarian cancer. Whether a possible association between height and ovarian cancer exists is unknown. We explored whether BMI and height were associated with ovarian cancer risk in a Norwegian cohort of approximately 1.1 million women, aged 14-74 years who were measured between 1963 and 1999. The cohort was followed for an average of 25 years through linkage to population-based cancer and death registries. Among the cohort, 7882 histologically verified cases of ovarian cancer were registered. Relative to women with a medium BMI (18.5-24.9 kg/m2), women who were overweight or obese in adolescence or young adulthood had an increased risk of ovarian cancer; women with a very high BMI in adolescence had a relative risk of 1.56 (95% confidence interval = 1.04 to 2.32) compared with women with medium BMI. No such association was seen in older women. A positive association between height and risk of ovarian cancer, particularly endometrioid ovarian cancer, was observed in women younger than 60 years of age.