This article examines the relationship between a set of demographic, socioeconomic, sociopsychologic, and health status characteristics of a heterogeneous adult population and their use of nonprescribed drugs. The objective is to determine whether nonprescribed drug use is best accounted for by demographic and socioeconomic factors, by health and medical beliefs, by health status, or by some combination of these. The data are derived from a personal interview survey of 2603 adult members of the Kaiser-Permanente Medical Care Program, Oregon Region. The results indicated that a combination of characteristics from among these three sets were the best predictors. Sex, income, education, mental health status, tendency toward self-treatment, and level of concern with health matters were the most important variables, although they account for only a small amount of the variation in nonprescribed drug use. A portrait of the most frequent users of nonprescribed drugs raised the question as to whether these are the classic neurotics, the "worried-well," or persons whose medical care needs have not been adequately recognized or met.