PURPOSE: Greater rates of lifetime drug use among the baby-boom generation, combined with the size of that generation, suggest that the number of elderly persons using drugs will increase in the next two decades. Given the potential public health demands implied by increasing numbers of elderly drug users, the goal is to project the numbers of current drug users aged 50 years and older in 2020. METHODS: Using the modeling and projection methods of Gfroerer et al (2003) applied to data from the 1999 to 2001 National Household Surveys on Drug Abuse, projections were developed for the use of marijuana, nonmedical use of any prescription-type psychotherapeutic drug, and any illicit drug use. RESULTS: From 1999 to 2001 to 2020, past-year marijuana use in persons 50 years and older is forecast to increase from 1.0% to 2.9%. The number of users is expected to increase from 719,000 to almost 3.3 million, reflecting the combined effects of the increase in rate of use and a projected 51.9% increase in the civilian noninstitutionalized population in this age group. Use of any illicit drug will increase from 2.2% (1.6 million) to 3.1% (3.5 million), and nonmedical use of psychotherapeutic drugs will increase from 1.2% (911,000) to 2.4% (almost 2.7 million). CONCLUSIONS: These projections call attention to changes to be considered in planning and to the need for improved knowledge of the biomedical and psychosocial effects of nonmedical drug use on aging and elderly individuals.