Up to 60 percent of adults report that they have had nocturnal leg cramps. The recurrent, painful tightening usually occurs in the calf muscles and can cause severe insomnia. The exact mechanism is unknown, but the cramps are probably caused by muscle fatigue and nerve dysfunction rather than electrolyte or other abnormalities. Nocturnal leg cramps are associated with vascular disease, lumbar canal stenosis, cirrhosis, hemodialysis, pregnancy, and other medical conditions. Medications that are strongly associated with leg cramps include intravenous iron sucrose, conjugated estrogens, raloxifene, naproxen, and teriparatide. A history and physical examination are usually sufficient to differentiate nocturnal leg cramps from other conditions, such as restless legs syndrome, claudication, myositis, and peripheral neuropathy. Laboratory evaluation and specialized testing usually are unnecessary to confirm the diagnosis. Limited evidence supports treating nocturnal leg cramps with exercise and stretching, or with medications such as magnesium, calcium channel blockers, carisoprodol, or vitamin B(12). Quinine is no longer recommended to treat leg cramps.