Obesity is a risk factor for breast and ovarian cancer; the mechanisms of action are not completely understood. Perturbed lipid metabolism often accompanies obesity; we therefore ascertained the associations between lipid components and breast and ovarian cancer risk in a prospective cohort study. A total of 234,494 women with baseline measurements of triglycerides and total cholesterol and glucose were selected from the AMORIS database.A total of 27,394 had measurements of high-density lipoprotein, low-density lipoprotein, apolipoprotein (Apo) B, and A-I. Associations between quartiles and dichotomized values of lipid components and breast and ovarian cancer risk were analyzed using Cox proportional hazard models. We identified 6,105 women diagnosed with breast cancer and 808 women diagnosed with ovarian cancer. A weak trend was observed between triglycerides and breast cancer (HR, 1.01, 95% Confidence Interval, 0.94-1.09; 0.93 (0.86-1.00) 0.91 (0.84-0.99), second, third, and fourth quartiles; P = 0.01). No other associations between lipid components and risk of breast cancer or ovarian cancer showed statistical significance. A weak protective association was found between levels of triglycerides and risk of breast cancer. An analysis including information on tumour characteristics of ovarian cancer and breast cancer may provide more insight in possible links between lipid metabolism and the risk of these cancers. ©2012 AACR.