Estrogen and Gallstones

The National Institute of Diabetes and Digestive and Kidney Diseases published this article on gallstones. In it they talk about some of the risk factors for gallstones. "Scientists believe cholesterol stones form when bile contains too much cholesterol, too much bilirubin, or not enough bile salts, or when the gallbladder does not empty as it should for some other reason."
Women are more at risk of gall bladder problems because Estrogen causes an increase in the cholesterol levels in the bile. Increased cholesterol levels in the bile leads to gallstone formationin addition to other problems such as gall bladder cancer.

http://digestive.niddk.nih.gov/ddiseases/pubs/gallstones/