More patients with ovarian cancer carry predisposing mutations, and in more genes, than previously thought. A rapid method for screening genomes has located 12 genes for ovary, fallopian tube and peritoneum cancers. More than one-fifth arose in women with a family history, but relying on family history would have missed one-third of cases. The sequencing method could become applicable to patient testing for a broad range of breast, colon, pancreatic and melanoma gene mutations.