This application requests support to initiate a research program directed to the familial nature of the use and abuse of alcohol, to assessment of age, gender, and social modulation of genetic influences on drinking during the critical developmental period from mid-adolescent to early adulthood, and to the early identification of familial and behavioral markers among those who are at risk for sustained abuse of alcohol. The research will use a unique resource: The Finnish Twin-Family Cohort, population-based, and linked to a nation-wide death, disease, and insurance registers. We propose a prospective study design in which five consecutive, nation-wide birth cohorts of adolescent twins, their siblings, parents, and selected siblings of both parents will be longitudinally studied. Over the course of a five-year period,> 12,500 members of 2,600 kinships of adolescent twins will be assessed with postal questionnaires. The study population will include > 1,600 pairs of like- sex twins, about 800 twin pairs of unlike sex, some 5,000 parents of these twins, and selected siblings of both twins and parents. All twins will initially studied within three months of their 16th birthday, with subsequent follow-up planned for age 18 and, in projected research, again at age 21. The baseline survey, at age 16, will occur when most Finnish adolescents are initiating social drinking; the first follow-up is timed when the twins are leaving home, separating from one another, beginning adult careers or their military service. Questionnaire content includes assessment of drinking habits, attitudes and expectancies toward alcohol, stressful life events, social support, and personality dimensions that are associated with early alcohol abuse. The twins' parents and uncles will be screened for alcohol-related disorders via linkage to the hospital discharge registries to identify adolescent twins at confirmed genetic risk. The research aims are (i) identification of genetic and environmental influences on initiation, continuity, and change in social drinking, (ii) modulation of these influences by age, gender, familial history of alcohol abuse, life events, and change in twins' social contact, and (iii) identification of individual and familial markers for sequencing from adolescent social drinking to adult abuse of alcohol. The revised application proposes broader assessment and behavioral problems associated with alcohol use and new structural modeling analyses for which two expert co-investigators have been added to the project staff.