Data on incidence, tumour size at diagnosis and mortality from breast cancer in the southeast of the Netherlands, collected by means of the SOOZ-cancer registry were studied in combination with data on patient management, collected through the regional tumour work group. Age-adjusted incidence increased by approx. 1% per year, especially in women less than 50 years and mortality showed a slight decrease in women less than 60 years. The proportion of patients with a tumour greater than 5 cm and with extension to chest wall or skin decreased from more than 40 to 15%. The proportion of tumours of 2.1-5 cm rose from 30 to 35% and that of less than or equal to 2 cm from 20 to almost 45%, in particular in younger women. The process of patient management changed by the shift to smaller tumours and the introduction of mammography, cytology and breast sparing treatment. These 'spontaneous' changes may have implications for the effectiveness of future breast cancer screening programs, which would only cover 35% of women with invasive breast cancer in this population.