Between 1974 and 1992, both inclusive, 204 renal adenocarcinomas were treated in the Urology Unit of the '12 de Octubre' Hospital, of which 54 (26.4%) were diagnosed by chance. The relative frequency of these renal tumours has experienced a highly significant progressive increase, from 0 in the 1974-1978 interval, to 13.04% in 1978-1980, 14.7% between 1981-1983, 20.68% in 1984-1986, 37.84% in 1987-1990, to reach over the last three-year period of 1990-1992 the remarkable figure of 41.93%. There has been no differences regarding incidence by sex (50% males and 50% females). Mean age at presentation is 61.5 years, ranging from 23 to 78 years. The suspected pathological cause most frequently leading to carry out the study where renal carcinoma is accidentally diagnosed are gastrointestinal disorders (50% of cases). The most frequently used imaging diagnostic technique is ultrasound (50% cases), emphasising the gradual increase in the number of cases diagnosed by ultrasound or CAT during the course of the study. Carcinomas accidentally diagnosed by CAT are those with less volume in our series. Regarding tumour characteristics, it should be pointed out a higher occurrence in the right kidney (64.8%) and a most frequent location in the upper renal pole (48%). Mean tumoral volume was 126 cc, although that value has gradually dropped, so that now the mean volume of accidental tumours treated over the last 5 is being 91 cc. Most cases present low staging at the time of diagnosis, 81% being pT2 N0 M0. Current overall survival is 89% of all cases followed-up.