STUDY OBJECTIVE: To estimate age dependent sensitivity and sojourn time in a breast cancer screening programme by different methods. POPULATION AND METHODS: The study population comprised women participating in the DOM project--the Utrecht screening programme for the early detection of breast cancer. Breast cancer screening prevalence data and incidence rates after a negative screen were used to estimate age specific sensitivity and mean sojourn time by different methods. MAIN RESULTS: Maximum likelihood estimates of the mean sojourn time varied from one year for women aged 40-49 years to three years for women over the age of 54. Sensitivity was calculated by two different methods. Both pointed to a high sensitivity (around 100%) in the age groups 40-49 and over 55 years. For women aged 50-54, the sensitivity varied from 63% to 100%, depending on the method used and the value of the baseline incidence rate. CONCLUSIONS: Different methods of estimating sensitivity pointed at an acceptable level in women over and under 50 years of age. Sojourn time, and thus the tumour growth rate, seemed to be age dependent. This could mean that the until now disappointing screening results in women under 50 years of age are not so much a result of low sensitivity as of a relatively high tumour growth rate in younger women.