Gallstones are common, affecting about one fourth of women and 10% to 15% of men over the age of 50. They are more prevalent in Amerindians and Mexican-Americans and less common in blacks. Principal risk factors are age, sex, and obesity. Lesser risk factors include childbearing, abstinence from alcohol, and some medications. The rate at which asymptomatic gallstones become symptomatic is low but significant, while patients with mildly symptomatic stones are at even greater risk for future pain and complications.