Hospital treatments are assumed to be a 'teachable moment'. This phenomenon, however, is only poorly conceptualised and untested. A stage-theoretical perspective implies that a cueing event such as hospital treatments is a teachable moment if a stage progression, change of cognitions, or both occur. This concept is examined in a cross-sectional study by comparing smokers in two treatment settings, an emergency department (ED) and inpatient treatment after elective surgery, with smokers in a control setting. Setting differences were hypothesised in stage distribution, and levels of and stage differences in social-cognitive factors under control for possible confounders. Stage, social-cognitive factors and possible confounders were assessed in 185 ED smokers, 193 inpatient smokers and 290 control smokers. Compared to control smokers, ED and inpatient smokers were in higher stages; they perceived fewer risks and cons; inpatient smokers reported more concrete plans. Stage differences in self-efficacy among ED and inpatient smokers differed from those among control smokers, but the former corresponded more strongly to the theoretical stage assumptions. The results suggest that hospital treatments lead to a stage progression and change of corresponding cognitions, and thus represent a 'teachable moment'. Stage-matched interventions should be provided but consider differences in cognitions to be effective.