To determine the role of sonography (US) in patients with renal colic, 40 patients were examined by means of US, plain abdominal film (PF), and intravenous pyelography (ivp). US sensitivity was 92.3% in diagnosing hydronephrosis and 75% in detecting calculi. Small calculi were correctly identified, irrespective of their chemical composition. It must be stressed how US, as compared to ivp, proved unsatisfactory in such cases as difficult visualization of the middle portion of the ureter, unsuccessful identification of acute obstructions without hydronephrosis (although the patient's hydratation may be useful in this respect), poor functional information (although there was a correlation between renal hyper-echogenicity and obstructive nephrogram). US is safe and easy to perform, and is suggested for the initial evaluation of patients with renal colic, together with PF, and as an alternative to ivp. Moreover, US is the ideal technique in the follow-up of these patients. Therefore, ivp should be performed in case of differing clinical and sonographic findings, when the calculus is not ejected within the expected time, and when surgery or lithotripsy are foreseen.