Objective: The goal of this study was to develop a factor score derived from measures of past-12-month alcohol consumption. Method: Data were drawn from two studies-the Adult and Family Development Project (N = 734) and the Missouri Adolescent Female Twin Study (N = 3,787). Data on four indices of alcohol consumption (quantity, frequency, frequency of drinking to intoxication, and frequency of five or more drinks/day) were factor analyzed, and differences in fac- tor loadings across gender, race/ethnicity, and study were tested. Cor- relations between these factors were computed across three assessments and between parent and offspring self-reports. Finally, using the classical twin design, variance in the past-12-month alcohol consumption factor was decomposed into additive genetic (A), shared environmental (C), and nonshared environmental (E) influences, and the extent to which these factors overlap with those influencing lifetime heaviest drinking were examined. Results: Factor loadings across all groups were high (.69-.95), with some evidence for differing factor loadings across gen- der, race/ethnicity, and study. The across-wave correlations for the factor ranged from.22 to.62. The within-wave correlation between parental and offspring drinking was.25, suggesting the importance of familial influences, which genetic analyses attributed to both additive genetic (31%) and shared environmental (17%) factors. The overlap between genetic influences on past-12-month and lifetime heaviest drinking was 0.97. Conclusions: A factor score derived from past-12-month drinking measures is heritable and is largely influenced by those genetic factors that influence heaviest drinking, at least in young adults. It also shows moderate across-wave stability. This will allow for large- and small-scale genomic studies to use past-12-month drinking measures in data analysis of similar cohorts. (J. Stud. Alcohol Drugs, 72, 444-452, 2011).