During the period from 1978-1984 the incidence of cancer among 2,465 male urban bus drivers in three major cities in Denmark was studied. The information with regard to cancer diagnosis was obtained from the Danish Cancer Registry. Danish men in 1981 were used as reference. Standardized Morbidity Ratio (SMR) for bladder- and skin cancer was significantly elevated among the bus drivers with values of 206 and 202, respectively. As to other cancers, no significant deviations from the expected were found. The same result was found when only drivers with more than ten years' seniority were included in the calculations. The incidence of skin cancer remained significantly elevated when corrected for degree of urbanization. Traffic density and whether the drivers worked in Copenhagen or in the province were not related to cancer incidence.