The relationship of urinary tract infection (UTI) to urolithiasis was studied in 1069 patients who were treated in the Department of Urology, Okayama University Hospital. Of 211 cases with known causative factors, 58 (27.5%) had UTI. The incidence of cloudy urine became higher with increasing age and was significantly higher in females with renal calculi than in males with renal calculi. The main organisms isolated from the urine were Pseudomonas, Staphylococcus, E. coli and Proteus. UTI, caluculi containing struvite, and proteus in the urine were fonud significantly more often in cases of stghorn caluculi than in cases of other renal calculi.