A 2-year-old girl with asymmetrical upper limbs and underdevelopment of the bones of the left forearm, wrist and hand with associated muscular and osteal hypoplasia is described. Doppler ultrasonography of the arterial trunks of the upper limb suggested a normal ulnar trunk in the left upper arm, an arterial vessel extending from the bend of the elbow to the distal third of the forearm, and the absence of any other arterial trunks in the radial region. Angiography confirmed that vascularization of the forearm was sustained by the ulnar artery, which supported the dorsal arch of the carpus and digital arteries arising from it. The interosseal artery was morphologically normal but there was aplasia of the radial artery. It is suggested that this malformation is the result of suppressed development of the vascular system of the left radial segment as other pathologies normally associated with the condition were absent.