We report on a 60-year-old man, seen at the emergency department because of severe left flank pain. Clinical diagnosis was that of renal colic. Overnight he became haemodynamically unstable and haematuria became massive, so multidetector CT (MDCT) was performed. MDCT with reconstructions can represent complex imaging findings in a more straightforward way compared with transverse images. Rupture of a renal artery aneurysm into the left pelvis was seen on coronal reconstructed CT images. Nephrectomy was performed. Rupture of a renal artery aneurysm into the pelvis is unusual and death is likely if diagnosis and treatment are delayed. The initial clinical presentation may be very similar to renal colic. MDCT allows timely and correct diagnosis of this unusual condition.