Hypothenar hammer syndrome is a rare and often incorrectly diagnosed form of secondary Raynaud's phenomenon in workers who use their hand as a hammer. We report 17 documented cases with long-term follow-up after diagnosis made on the basis of arteriography. Clinical findings include male sex, unilaterality, sudden onset, and severe Raynaud's phenomenon. Angiography indicated that the 17 patients had either ulnar thrombosis or ulnar aneurysm; most of them also had embolic occlusions of the digital arteries. Main pathologic findings were thrombosis on the intima and fibrosis in the media. We adopted a surgical procedure consisting of resection with end-to-end reconstruction for patent aneurysms to avoid downstream emboli and more conservative treatment when the ulnar artery was thrombosed. No patient required digital amputation and all except one improved and were able to live and work normally with only a moderate disability, consisting of Raynaud's phenomenon during the cold season only.