Using three different registers a cohort study was undertaken to describe the relationship between type of occupation and hospitalization. A total of 958 096 subjects aged 20-64 years were followed-up for one year regarding inpatient care. Several significant associations between type of occupation and incidence of hospitalization for different diagnoses were observed. Male subjects employed in occupations where a high proportion reported a combination of hectic work and few possibilities to learn new things were more frequently hospitalized for myocardial infarction than other working men. The relative 'hospitalization' ratio for men 20-54 years of age in these strenuous occupations was estimated as 1.6 with a 95% confidence interval of 1.3-1.9. For women, the relative 'hospitalization' ratio in the ages 20-64 in occupations where a high proportion reported a combination of hectic and monotonous work was estimated as 1.6 with a 95% confidence interval of 1.1-2.3. Both these associations were statistically significant even after controlling for 12 possible confounding factors.