Despite the potential importance of delineating the development of alcohol use over the adolescent years, detailed investigations of incremental increases in alcohol use in adolescence are rare. Age- and gender-related differences in frequency, quantity, patterns, and consequences of alcohol use were examined among 1,260 male and 1,338 female adolescents at 6-month age intervals between 11.5 and 17.5 years. The results indicated age-related increases in alcohol use for both sexes. The greatest shift toward increased use occurred between the ages of 14 and 15 years. By age 15, the percentage of non-alcohol users had dropped to 20 percent from 63 percent at age 12, and the percentage of frequent users of substantial quantities of alcohol had risen from 1 percent at age 12 to 19 percent at age 17. Sex differences occurred only for the pattern of frequent use or use of substantial quantities, with greater use reported by older males. Greater use was reported in a 1982 cohort than in a 1981 cohort. The findings suggest that primary prevention efforts should occur before age 13, with secondary prevention efforts in the middle to late teenage years. (NRB)