Rationale: There has been little study of the very early time course of the smoking withdrawal syndrome, despite its relevance to the maintenance of both smoking and postcessation abstinence. The literature contains a range of estimates about the early appearance of withdrawal symptoms, but without reference to empirical data. Objectives: The study aim was to conduct a comprehensive, multimodal assessment of the early time course of the symptoms associated with smoking withdrawal among cigarette smokers. Methods: Participants were 50 smokers randomly assigned to either abstain or smoke at their own pace during 4 h in the laboratory. Dependent measures included resting heart rate, sustained attention (Rapid Visual Information Processing task; RVIP), selective attention to smoking stimuli (an emotional Stroop task), and self-report (Wisconsin Smoking Withdrawal Scale; WSWS). After baseline assessment, participants were assigned to the two conditions and the dependent measures were collected every 30 min. Results: Generalized estimating equations revealed that abstaining participants displayed greater withdrawal than smoking participants on all measures with the exception of the Stroop task. Statistically significant differences in withdrawal were found within 60 min on heart rate, within 30 min on the RVIP, and between 30 and 180 min postcessation on the various subscales of the WSWS. Conclusions: These findings provide the first evidence of the early time course of smoking withdrawal symptoms, although further research is needed to distinguish withdrawal from drug offset effects. Implications for understanding the maintenance of daily smoking and for the treatment of tobacco dependence are discussed. © Springer-Verlag 2006.