A 66-year-old woman presented with back pain and arm claudication. Severe stenosis of the left proximal subclavian artery was detected incidentally by thorax computed tomography. Doppler ultrasonography and phase contrast magnetic resonance angiography (PCMRA) evaluation revealed partial subclavian steal. The stenosis was successfully treated with percutaneous stenting. Imaging findings are described and a brief review of the literature emphasizing the role of PCMRA in diagnosing partial steal is discussed. © 2011 Japan Radiological Society.