BACKGROUNDS: Stone analysis is essential to determine the possible cause of stone formation and treatment of urolithiasis. Physical analysis using Fourier transform infrared spectroscopy(FT-IR), compared to chemical analysis, requires minimal sample volume, shows uniform sensitivity and specificity to all components and provides quantitiative results with greater reproducibility. We compared urinary stone analysis using FT-IR and chemical ananlysis. METHODS: From January 1996 to May 1999, 515 urinary stones were analyzed. For physical anlaysis, we used FT-IR system 2000(Perkin-Elmer Co., U.S.A.) and SpectrumTM software(Perkin-Elmer Co., U.S.A.). Chemical analyses for calcium, phosphate, uric acid, carbonate, magnesium, ammonia, oxalate and cystine were performed. Stone analyses with FT-IR were compared to those with chemical analysis. Clinical findings and the other laboratory findings including routine urinalysis, serum tests, and 24 hour urine test were also investigated. RESULTS: We analyzed 515 urinary stones from 501 patients. Sex ratio was 2.8: 1 and mean age was 48 years. Physical analyses were performed in 515(100%) stones and 81.2% of them showed mixed composition. And 79.4% included calcium oxalate monohydrate or dihydrate. Calcium oxalate monohydrate(63.3%), uric acid(11.3%), calcium oxalate dihydrate(9.9%), and carbonate apatite(8.3%) were commonly found as a major component. Chemical analyses could be done in only 454 cases(88.2%) due to insufficient sample and the most common positive findings were calcium(50.0%), phosphate(33.0%), and uric acid(18.5%). Seventy-one cases(15.6%) with negative chemical reactions to all components were mixed stones except 9 cases. When the stone components were analyzed by FT-IR and chemical method, we found full agreements in only 2.3%, partial agreements in 56.3%, poor agreements in 11.5% and no agreements in 4.3% of total cases. Hypercalciuria and natriuresis were found in 36.1% and 23.0%, respectively. The pH of urine shows significant differences in uric acid and struvite stones compared to the pH of the others(P<0.05). CONCLUSIONS: We found difficulties in detecting minor or mixed components of urinary stone and in analyzing small sized stone by chemical methods. Physical analysis using FT-IR can provide more accurate determinations of composition of urinary stones and can be significantly useful in diagnosis, treatment and prevention of urolithiasis.