Very little research has been conducted on what time window provides a representative picture of daily drinking. With respect to pretreatment drinking, one study that used the Timeline Followback (TLFB) with problem drinkers found that a 3-month window is generally representative of annual pretreatment drinking. The objective of the present study was to determine the shortest representative time window for reports of annual posttreatment drinking. A second objective was to determine which of two time windows, 90 days from the end of treatment or 90 days prior to the end of follow-up, was the most representative proxy for annual posttreatment drinking. TLFB reports from 467 problem drinkers who participated in a randomized controlled trial of a mail-based intervention were used in the present analysis. The results show that a 3-month posttreatment window (i.e., first 90 days after the intervention) is sufficiently representative (r = .94) of annual posttreatment drinking for problem drinkers (i.e., less severely dependent alcohol abusers). In addition, although there were no clinically significant differences in drinking behavior between the two 90-day posttreatment windows, the use of proximal windows (i.e., closer to the end of treatment) would minimize participant attrition. In addition, a 3-month versus 12-month TLFB follow-up time frame resulted in a much higher percentage of participants completing the full TLFB (89% vs. 71%). Further research is needed to determine if these findings will generalize to more severely dependent alcohol abusers.