The authors compared the value of sonography with I.V. urography and CT in the diagnosis of nephrolithiasis, employing a retrospective study conducted on 310 patients. False positive and false negative sonographic findings were analysed in retrospect and the differential diagnosis discussed. Sonography proved of equal value to I.V. urography. 90% correct diagnoses were made via sonography; its sensitivity was 89%, its specificity 91%. 29% of the sonographically correctly diagnosed kidney stones had been detected by chance. The smallest sonographically identified stone was 3 mm, whereas the biggest stone that had been missed out was 7 mm. Sonography is definitely superior to I.V. urography in the detection of nephrocalcinosis and of roentgen-negative stones. Sonographically questionable parenchymal calcifications without shadowing should be investigated further by CT in case of clinical significance, even if the plain film is negative. The number of false positive findings in sonography can thus be reduced. Sonographic differentiation between central parenchymal calcification and stone formation is difficult in rare cases only. If required, additional information can be obtained via I.V. urography. The authors recommend sonography as the method of choice for suspected nephrolithiasis before I.V. urography is performed.