The aging "baby boomer" population has higher rates of substance use than previous cohorts and is predicted to put increased demands on substance abuse treatment services; however, little is known about older illicit drug abusers. This study compared 41 older (age 50-66 years) and 26 younger (age 25-34 years) opioid maintenance patients on psychiatric, substance use, medical, general health, demographic, and psychosocial characteristics using standardized instruments. The health of both groups was compared to age and sex-matched U.S. population norms. Both groups had high rates of lifetime psychiatric and substance abuse/dependence diagnoses, and poor general health compared to population norms. The older group began using illicit substances significantly later in life, and had significantly more medical problems and worse general health than the younger group. The inevitable increasing medical morbidity and physical limitations of an increasingly large older population with substance use problems will challenge treatment providers and planners. Low rates of positive urine opioid tests occurred for both older and younger patients without age-specific services.