An intrinsic-extrinsic model of motivation for smoking cessation is extended to a population-based sample of smokers (N = 1,137), using a previously validated Reasons for Quitting (RFQ) scale. Psychometric evaluation of the RFQ replicated the model that includes health concerns and self-control as intrinsic motivation dimensions and immediate reinforcement and social influence as extrinsic motivation dimensions. Compared to volunteers, the population-based sample of smokers reported equivalent health concerns, lower self-control, and higher social influence motivation for cessation. Within the population-based sample, women compared to men were less motivated to quit by health concerns and more motivated by immediate reinforcement; smokers above age 55 expressed lower health concerns and higher self-control motivation than smokers below age 55. Higher baseline levels of intrinsic relative to extrinsic motivation were associated with more advanced stages of readiness to quit smoking and successful smoking cessation at a 12-month follow-up. Among continuing smokers, improvement in stage of readiness to quit over time was associated with significant increases in health concerns and self-control motivation.