Responses were received from 15,268 randomly selected military personnel to a self-administered anonymoous questionnaire. Items on the questionnaire generally focused on the frequency and amount of nonmedical drug and alcohol use, reasons for use or nonuse, and consequences of use in terms of adverse effects on the individual's well-being and job performance. Following a pilot test, the field survey was conducted during February-April 1980. Drugs most commonly used were marijuana and hashish, nonmedical drug use by military personnel other than enlisted personnel in the E1-E5 ranks was rare, and an estimated 3 percent of junior enlisted personnel were physiologically drug-dependent. The type of work impairment most frequently reported by junior enlisted personnel was high while working. Most military personnel drank alcohol at least occasionally. In general, the highest prevalence of alcohol consumption was recorded by senior officers, followed by junior officers, junior enlisted pesronnel, senior enlisted personnel, and warrant officers. Beer was the most commonly consumed beverage among 73 percent of all military personnel. Hard liquor was consumed by 51 percent of respondents within the past 30 days, but only 8 percent drank hard liquor as often as 3 times a week. About 21 percent of respondents engaged in heavy beer drinking at least once a week during the past 12 months; comparable figures for wine and hard liquor were 5 percent and 11 percent, respectively. An estimated 7 percent of military personnel were alcohol-dependent during the preceding 12 months. Lowered performance was the type of work impairment most frequently reported. Recommendations for additional research are offered. Appendixes contain further information on drug and alcohol consumption by military personnel and the study questionnaire. 27 tables