Computed tomography (CT) is the most informative investigation used to examine stones in the urinary system. CT examination has a great ability to detect urinary calculi, differentiate them with other ureteral obstructions and identify other possible, non–urological causes of low back pains. Since 1980, the extracorporeal shock wave lithotripsy (ESWL) has become one of the main methods of treatment of reno-ureteral lithiasis. Not all renal calculi are easily broken with ESWL. The ESWL results depend on various factors, such as the reno-ureteral calculi sizes, location, chemical composition, fragility, lithotripter type, the presence of an obstruction or infection. The aim of the study is to estimate the density of urinary calculi at patients with renal lithiasis that require ESW treatment. The study will estimate the efficacy of ESWL utilization based on the size and density of reno-ureteral calculi assessed at CT. In addition to the size and location of the stone and the overall health of the kidney, CT can assess the density of the stone in Hounsfield Units (HU). The HU, measured by CT is related to the density of the tissue or stone. The most recent reports have suggested that the HU value and its variants facilitate prediction of stone composition. Some stu demonstrate that the chemical composition of calculi has become an important factor in the urolithiasis treatment by ESWL. Urinary calculi with densities <1000 HU respond better to ESWL treatment. Thus, if the density of the stone is high, then the shock wave energy is using stronger, to obtain a good fragmentation of calculi. A recent study determinated that a stone with size >4mm, HU≤500 and pH≤ 5.5, in 90% of cases was found to be uric acid stones who have significant success through ESWL treatment. Studies performed to date suggest that these values would make a significant contribution to the diagnosis and treatment of urinary system stones. However, more data are required to assess this further. The CT densitometry is a nonivasive method and its use prior to ESWL can help determine the average calculus density, which can detect the fragility, hence the treatment outcome. Previous studies have revealed the benefit of HU values, parameters obtained from CT scans, on ESWL treatment and predicting the composition of urinary system stones. Also, exact information about the calculus density may help finding the most optimal treatment method from the beginning.