9 consecutive cases of Legionnaires' disease are presented, all of which involved either a pathological urinary sediment or acute renal insufficiency. Diabetic glomerular sclerosis and terminal septic shock in one patient accounted per se for the urinary findings and terminal oliguric renal failure. In the remaining 8 patients the renal abnormalities are interpreted as manifestations of Legionnaires' disease: these were acute renal insufficiency in 6, requiring dialysis treatment in 4, proteinuria in 7, hematuria in 5, leukocyturia in 5 and cylindruria in 3 patients. One patient died of pneumonia and one patient, without Legionella-related renal involvement, of septic shock. Renal histology of 5 patients showed acute interstitial nephritis in one and diffuse sclerosing interstitial nephritis in a second patient, whose biopsy was obtained after 3 months' hemodialysis treatment. In 3 patients renal biopsy findings were explained by preexisting renal pathology, i.e. diabetic nephropathy, chronic transplant rejection and shock kidney respectively. Renal failure requiring hemodialysis and urinary abnormalities were largely reversible.