During recent years, the relationship between exposure to magnetic fields and cancer has attracted increasing interest. In Sweden, train personnel are exposed to comparatively strong magnetic fields in their work. The aim of the present study was to investigate cancer incidence, particularly leukemia and brain tumors, among male railway engine drivers and conductors, respectively, and to compare their cancer incidence with that of the general male population. The study population comprised all male railway engine drivers (n = 7,466) and conductors (n = 2,272) who were ever employed at the Swedish State Railways during the period 1976-90. The study population was observed with regard to cancer incidence by means of the National Cancer Register for the period 1976-90. The total cancer incidence (all tumors included) among railway engine drivers was lower than in the general Swedish population. An increased incidence of lymphocytic leukemia was observed among railway engine drivers and conductors combined (relative risk = 2.3; 95 percent confidence interval = 1.3-3.2), with the same point estimate for both occupational groups. For brain tumor (astrocytoma), the observed relative risk was close to one. The study provides evidence of an excess risk of lymphocytic leukemia in railway engine drivers and conductors, workers with known occupational exposure to magnetic fields.