BACKGROUND High work stress could decrease physical activity but the evidence of the relationship has remained equivocal. The present study examined the association between job strain and leisure-time physical activity in a large sample of employees. METHODS Cross-sectional data related to a cohort of 46,573 Finnish public sector employees aged 17-64 years. Job strain was measured by questions derived from Karasek's Demand/Control model. Leisure-time physical activity was defined using activity metabolic equivalent task (MET) index. Analysis of variance was used to compare means of MET-hours/week by job strain categories and by tertiles of job control and job demands. RESULTS Women and men with high strain (low control and high demands), passive jobs (low control and low demands), and low job control had 2.6 to 5.2 MET-hours/week less than their counterparts with low strain and high control, respectively, even after the effects of age, marital status, socioeconomic status, job contract, smoking, heavy drinking, and trait anxiety were taken into account. Active jobs (high control and high demands) were additionally associated with lower mean of MET-hours in men and in older workers. CONCLUSIONS Our findings suggest an independent, albeit substantially weak, association between higher work stress and lower leisure-time physical activity.