The test-retest reliability of male (n = 40) and female (n = 40) college students' reports of recent drinking behavior was evaluated using a timeline (TL) procedure. The students also completed a quantity-frequency (QF) questionnaire (Cahalan, Cisin, & Crossley, 1969) often used to categorize subjects' drinking histories in alcohol research studies. The TL-derived data were found to have generally high reliability (usually r's greater than or equal to .87) for both males and females, with males having slightly higher reliabilities overall. Subjects were classified into drinker categories based on the QF questionnaire answers, and the resulting groups were compared using their TL-derived data on quantity, frequency, and quantity X frequency (mean number of drinks per drinking day) measures of drinking. The drinking behavior of subjects (as assessed by the TL) had great variability within the QF categories, and there was extensive overlap between subjects classified by the QF method as heavy, moderate and light drinkers. Thus, QF categorization provides a relatively insensitive measure of individual differences in drinking behavior as compared to TL-derived data. The TL method also can be used to generate a variety of potentially useful dependent variables, whereas the QF method generates a single variable.