We find that five observable measures of substance use can be combined to form a single scale of drug use. An unrestricted latent class model specifies assignment of respondents to three categories based on their pattern of responses to items on the use of alcohol, marijuana, hallucinogens, cocaine, and pills such as barbiturates. Tests of external validity examining levels of association with independent variables such as attitudes toward the law, attachment, and religiosity are conducted, comparing the latent class scale with an additive scale of drug use. Levels of association are generally increased moderately utilizing the latent class scale. Finally, a modified Guttman scale is fit, assessing the pattern of progression of drug use from more commonly used drugs such as alcohol to the less commonly used drugs such as cocaine and hallucinogens.