Six-month posthospitalization follow-up data were collected from 52 alcoholic subjects and their collateral informants. Subjects' self-reports and collateral reports of subjects' drinking were highly correlated when subjects had been either mostly abstinent or mostly drunk throughout the follow-up period. When subject and collateral reports differed, there was no systematic direction of difference in number of abstinent days, but subjects reported fewer drunk days and more limited-drinking, hospitalization, and jail days than did their collaterals. Number of days that collaterals were in contact with subjects during the follow-up period was not strongly related to the amount of discrepancy between subject and collateral reports. These findings suggest that (a) alcoholics who have been hospitalized for detoxification generally provide reliable self-reports of their posttreatment drinking behavior, and (b) gathering data from collateral informants is an effective method for corroborating alcoholics' self-reports of drinking behavior.