We report the incidence and features of small cystic and noncystic noninflammatory renal lesions found in a series of 500 unselected necropsies performed for forensic reasons in a Portuguese population. A total of 997 kidneys was sectioned serially in 0.2 cm. sections. There were 1,256 lesions (the large majority being less than 1 cm.) found in 380 examined organs belonging to 265 cases. A total of 1,105 cystic lesions was observed in 195 (39 per cent) specimens, 108 medullary fibrous nodules in 89 (17.8 per cent), 29 cortical adenomas in 20 (4 per cent), 5 leiomyomas in 5 (1 per cent), 4 lipomas in 4 (0.8 per cent), 2 fibromyolipomas in 2 (0.4 per cent) and 3 fibromas of the capsule in 3 (0.6 per cent). Cystic lesions showed an increase in number with patient age, which does not occur with medullary fibrous nodules. Cortical adenomas were most frequent at the fifth and sixth decades of life. The risk of malignancy, with the possible exception of some of the cortical adenomas, is believed to be small.