Mexican Americans have an elevated risk of gallstones. Their increased rates may be due to genetic admixture with Native Americans, who have extremely high prevalences of cholelithiasis. Native Americans are believed to have almost exclusively cholesterol stones, whereas only 73% of non-Hispanics are reported to have such stones. Hence we hypothesized that Mexican Americans would have a higher proportion of cholesterol stones than would non-Hispanic whites. We interviewed 398 Mexican Americans and 93 non-Hispanic whites undergoing cholecystectomy and analyzed the composition of their gallstones. Mexican Americans were younger than non-Hispanic whites (P < 0.05). However, the age-sex standardized proportion of cholesterol stones was 89.7% in Mexican Americans and 87.2% in non-Hispanic whites. We conclude that Mexican Americans and non-Hispanic whites have gallstones of similar composition. The higher stone prevalence of Mexican Americans may be due to factors that predispose to both cholesterol and pigment stones.