Radiotherapy patterns were determined in all 34,487 cancer patients diagnosed between 1975 and 1989 in south-eastern Netherlands, a densely populated and prosperous area with a greying population of almost 1 million inhabitants. Specialised care was available in 10 community hospitals with expanding staffs and in a non-academic radiotherapy centre, the distance never exceeding 50 km. With respect to western Europe the cancer incidence rates for this area were relatively high for males and average for females during this period. We computed overall and tumour-specific percentages of patients receiving radiotherapy as primary treatment (RT1a) and estimated this for initial treatment of recurrence or metastasis (RT1b). The total number of patients receiving RT1a increased by about 2% per year, but age-adjusted figures remained stable at 36% for females and increased from 28% to 32% for males. Since 1986 about 40% of all new cases receive RT1a and RT1b and about 40% of all RT1a undergo secondary radiotherapy for recurrence or metastasis. Of all male and female patients 70% and 50%, respectively, were over 60. Diverse underlying tumour-specific trends in RT1a were observed: children and adolescents with cancer received RT1a less often (25% vs. 40%) as did patients with cervical (55% vs. 80%), ovarian (9% vs. 17%), small cell lung (25% vs. 55%) and non-melanoma skin cancer (5% vs. 55%); patients with stage 1 breast (70% vs. 45%), rectal (30% vs. 10%) and prostate cancer (31% vs 13%) and adenocarcinoma of the lung (40% vs. 20%) received RT1a more often.(ABSTRACT TRUNCATED AT 250 WORDS)