This is a cohort study of the mortality among chimney sweeps in Copenhagen, Denmark, during 1958-77. Nearly all the chimney sweeps started in the trade around the age of 15, and so this age gives the time of first exposure to the environmental conditions of the trade. The analysis applies a continuous time model with stratification by cause of death (cancer, non-cancer), time and age, where cumulative mortality rates are derived from current mortality tables. For each stratum of interest the observed/expected mortality ratio (O/E ratio) is calculated and a test performed, based on the normal distribution. The main result is a significantly higher cancer mortality for the 40-69 year age class compared with the population at large (O/E ratio = 3.9).