According to relapse models, self-efficacy (SE), or confidence in one's ability to abstain, should predict the outcome of an attempt to quit smoking. We reviewed 54 studies that prospectively examined this relationship. The relationship between SE and future smoking depended upon the population studied and the timing of the SE assessment. The relationship between SE and future smoking was modest when SE was assessed prior to a quit attempt; SE scores were .21 standard deviation units (SD) higher for those not smoking at follow-up than for those who were smoking. The relationship was stronger (.47 SD) when SE was assessed post-quit. However, this effect was diminished when only abstainers at the time of the SE assessment were included in analysis (.28 SD). Controlling for smoking status at the time of SE assessment substantially reduced the relationship between SE and future smoking. Although SE has a reliable association with future abstinence, it is less robust than expected. Many studies may overestimate the relationship by failing to appropriately control for smoking behavior at the time of the SE assessment. (PsycINFO Database Record (c) 2009 APA, all rights reserved).