Objectives To determine the total cancer incidence in relation to a 5-year exposure to caesium-137 (¹³⁷Cs) from the 1986 Chernobyl nuclear power plant accident.

Methods A closed cohort was defined as all individuals living in the three most contaminated counties in mid-Sweden in 1986. Fallout of ¹³⁷Cs was retrieved as a digital map from the Geological Survey of Sweden, demographic data from Statistics Sweden, and cancer diagnosis from the National Board of Health and Welfare. Individuals were assigned an annual ¹³⁷Cs exposure based on their place of residence (1986–1990), from which 5-year cumulative ¹³⁷Cs exposures were calculated, accounting for the physical decay of ¹³⁷Cs and changing residencies. HRs were adjusted for age, sex, rural/non-rural residence and pre-Chernobyl total cancer incidence.

Results The 734 537 people identified were categorised by exposure: the first quartile was low exposure (0.0–45.4 kBq/m²), the second and third quartiles were intermediate exposure (45.41–118.8 kBq/m²), and the fourth quartile was the highest exposure (118.81–564.71 kBq/m²). Between 1991 and 2010, 82 495 cancer cases were registered in the 3 counties. Adjusted HRs (95% CI) were 1.03 (1.01 to 1.05) for intermediate exposure and 1.05 (1.03 to 1.07) for the highest exposure compared to the reference exposure.

Conclusions We found a small overall exposure–response pattern of the total cancer incidence related to ¹³⁷Cs after adjustment for age, sex, rural residence and pre-Chernobyl cancer incidence.