Objectives.: This study examined the associations of left ventricular mass with self-reported cocaine and alcohol use prevalent in the young adult population. Background.: Increased left ventricular mass has been associated with long-term use of cocaine and alcohol; however, few of the published studies have been population based. Methods.: Data from 3,446 black and white participants (mean age 29.9 years) in the Coronary Artery Risk Development in Young Adults (CARDIA) study were used to examine the associations between echocardiographically measured left ventricular mass obtained from 1990 to 1991 and self-reported cocaine and alcohol use. Categories of cocaine use were those who denied ever using cocaine (n = 2,122), experimental users who admitted to cocaine use only 1 to 10 times in their lifetime (n = 755) and recurrent users who admitted to cocaine use > 10 times in their lifetime (n = 568). For alcohol consumption, categories were abstainers who consistently denied any alcohol consumption in the year before each of the three CARDIA examinations (n = 275), occasional users who admitted consuming alcohol less than once a week or not at all during the year before the third examination (n = 1,322), moderate users who consumed 1 to 209 ml of alcohol/week during the year before the third examination (n = 1,524) and heavy users who consumed ≥210 ml of alcohol/week during the year before the third examination (n = 323). Estimated power to detect a 10% difference in left ventricular mass between groups was >80%. Results.: For white women, left ventricular mass was significantly higher among those who reported 1 to 10 lifetime uses of cocaine than in never-users (128.5 g [SE 2.0] vs. 122.7 g [SE 1.4], p = 0.002). There were no other significant differences in left ventricular mass among categories of cocaine or alcohol use in unadjusted analyses or among analyses controlling for age, body mass index, alcohol or cocaine use, physical activity, cigarette smoking status and systolic blood pressure. Conclusions.: At the levels of consumption reported, neither cocaine nor alcohol use was associated with left ventricular mass in this cohort of healthy young adults. © 1995 American College of Cardiology.