BACKGROUND: Based on studies published so far, the protective effect of physical activity on stroke remains controversial. Specifically, there is a lack of insight into the sources of heterogeneity between studies. METHODS: Meta-analysis of observational studies was used to quantify the relationship between physical activity and stroke and to explore sources of heterogeneity. In total, 31 relevant publications were included. Risk estimates and study characteristics were extracted from original studies and converted to a standard format for use in a central database. RESULTS: Moderately intense physical activity compared with inactivity, showed a protective effect on total stroke for both occupational (RR = 0.64, 95% CI: 0.48-0.87) and leisure time physical activity (RR = 0.85, 95% CI: 0.78-0.93). High level occupational physical activity protected against ischaemic stroke compared with both moderate (RR = 0.77, 95% CI: 0.60-0.98) and inactive occupational levels (RR = 0.57, 95% CI: 0.43-0.77). High level compared with low level leisure time physical activity protected against total stroke (RR = 0.78, 95% CI: 0.71-0.85), haemorrhagic stroke (RR = 0.74, 95% CI: 0.57-0.96) as well as ischaemic stroke (RR = 0.79, 95% CI: 0.69-0.91). Studies conducted in Europe showed a stronger protective effect (RR = 0.47, 95% CI: 0.33-0.66) than studies conducted in the US (RR = 0.82, 95% CI: 0.75-0.90). CONCLUSIONS: Lack of physical activity is a modifiable risk factor for both total stroke and stroke subtypes. Moderately intense physical activity is sufficient to achieve risk reduction.