The authors examined estimated blood alcohol concentrations (BACs) reached by so-called "binge drinkers" and "nonbinge drinkers" using a survey of young adults (age 18-24 years) in Montana. One third of drinkers were classified as "binge drinkers" the last time they consumed alcohol, using a gender-specific definition commonly applied to young adults: for men, having 5 or more drinks in a row, and for women, having 4 or more drinks. BAC levels were estimated on the basis of length of drinking episode, gender, weight, and typical alcohol consumption level. Among "binge drinkers," 63% did not reach .10% BAC or higher, 48% did not reach .08% BAC or higher, and 30% did not reach .06% BAC or higher. Of the "nonbinge drinkers," 7% reached .06% BAC or higher and 4% reached .08% BAC or higher. These findings underscore the potential problem of using binge drinking as a description and shorthand measure of drinking to intoxication.