Quitting smoking benefits older individuals, yet there are few recent data describing older smokers. The goal of this paper was to test a series of hypotheses about differences between smokers age 50 years and older (50 + ) and those younger than age 50 (<50), presenting to the same treatment facility during 2002-2004 for participation in two randomized clinical trials: one exclusively for smokers age 50 + , and a second open to smokers age18 and older. As predicted, smokers age 50 + were more tobacco dependent, had better psychological functioning, and poorer physical functioning than those <50. Contrary to predictions, there were no differences in motivation to quit cigarette smoking or in alcohol use. Women age 50 + were less likely to report marijuana use than women <50, and less likely to receive a positive diagnosis for alcohol abuse then men. Despite higher scores on measures of tobacco dependence, older smokers were less likely to be diagnosed as tobacco dependent or having tobacco withdrawal using DSM-IV criteria. Rates of DSM-IV alcohol abuse and dependence were high in both age groups but were higher for smokers <50. There were no striking differences between studies in reasons for exclusion, but in both, the proportion of individuals excluded due to current antidepressant use was high. Implications for the assessment and treatment of older adults are discussed.