In many countries prostatectomy is one of the most common surgical operations in elderly men. We used administrative data for the entire male population of Denmark to study temporal and regional variations in the use of prostatectomy from 1977 to 1985. The total annual number of prostatectomies increased by 43% during the period, when the transurethral procedure (TURP) gradually replaced traditional open surgery. TURP accounted for 56% of all operations in 1977 but increased its share to 92% in 1985. Substantial regional variations occurred with index values for prostatectomy in 72 recruitment areas ranging from 0.56 to 1.62 (SCV x 100 = 5.3). The amount of variation decreased during the process of technology diffusion, but remained at a relatively high level (as in other countries) even after the process had been completed (SCV x 100 = 5.1).