Introduction: Knowing the composition of a urinary calculus is frequently a key factor in determining its most appropriate management. Helical computed tomography (CT) can provide helpful information on stone size and stone composition. Objectives: We sought to determine the urinary stone composition by CT characteristics. Materials and Methods: Since March 2008 till August 2009, 120 renal stones were obtained from patients who had undergone pyelolithotomy or nephrolithotomy at the Imam-Ali hospital, Zahedan, Iran. Stones with the largest diameter more than or equal to 5 mm were studied. Each calculus was placed inside the chicken lean meat. The radiologist was unaware of the exact chemical composition of the stones. We used independent sample t test for comparison of the absolute Hounsfield unit (HU) values of the different types of calculi. Results: Of total 120 participated patients, 67 (55.8%) were male and 53 of them (44.2%) were female. The mean age of cases was 35.8 ± 12.4 years. According to HU in CT scan and final confirmation with chemical analysis, the calculi were classified into several groups. Of 120 stones, 112 were chemically pure and 8 were mixed. There were 59 calcium oxalate, 27 calcium phosphate, 17 uric acid, 5 struvite, 4 cysteine and 8 mixed stones with variable ratios. In the analysis of the stones, overall difference between densities of the stones was statistically significant (P < 0.001). Conclusion: According to the result of our study, we concluded that the use of non-contrast CT can be helpful in the prediction of urinary stone composition
