INTRODUCTION: Dilatation of the collecting system requires differential diagnosis. Megacalycosis should be consi-dered in the differential diagnosis of congenital hydronephrosis. Congenital megacalycosis is a rare condition con-sisting of caliceal dilatation without ureteral obstruction. The abnormality is usually unilateral and kidney function is normal. CASE PRESENTATION: We report a male patient with urinary tract infection and dilatation of collecting system in the left kidney detected in ultrasound. Voiding cystourethrography ruled out vesicoureteral reflux. Dynamic renal scintigraphy showed hydronephrosis. Megacalycosis was suggested by lower-dose computed tomography urography. CONCLUSION: The diagnosis of megacalycosis prevented unnecessary diagnostic procedures and treatment.