It is often assumed that many alcoholics underreport their drinking and behavioral problems. Nonetheless, previous studies using official records and collateral reports suggest that self-reports of concrete drinking problems are not biased, and that overreports equal or exceed underreports. New data are presented, based on collateral reports and blood alcohol measures for 632 alcoholics interviewed four years after treatment. Results indicate that the subjects accurately reported abstention and major alcohol-related events, such as jail terms and hospitalization. Compared with estimates from blood alcohol measures, 35% of recent drinkers underreported their consumption during the 24 hours before the interview, and 24% underreported their consumption during the previous month. However, an overall outcome classification based on a combination of consumption and other measures was not substantially affected by errors in consumption reports. These findings indicate that most types of self-reports are valid, and that broadly based outcome measures are not likely to be significantly biased by underreporting errors.