Muscle cramps are characterized by a sudden, painful, involuntary contraction of muscle. Medical history, physical examination, and laboratory test help to determine the various causes of muscle cramps. Primary (or idiopathic) muscle cramps, without known cause, occur normally in healthy persons. Despite the „benign“ nature, many patients find idiopathic cramps very uncomfortable. They are frequent especially in elderly and pregnant women, presenting usually at night as nocturnal leg cramps. Secondary muscle cramps are not so frequent. They are caused by multiple divers causes: 1. Neurogenic disorders - amyotrophic lateral sclerosis, bulbospinal amyotrophy, polyneuropathies, radiculopathies, acquired neuromyotonia. 2. Muscle disorders - metabolic myopathies, dystrophinopathies, caveolinopathies, etc. 3. Systemic disorders - diabetes, hypothyroidism, cirrhosis, electrolyte disturbances, uremia, etc. 4. Drug and toxin induced cramps - statins, fibrates, diuretics, ethanol, etc. The first diagnostic step in a patient with muscle cramp is to find out if the cramps are of primary or secondary origin. Treatment of primary muscle cramps is empiric (antiepileptics, magnesium, stretching exercises). In patients with secondary muscle cramps the pathogenic therapy of underlying disease is of crucial importance. This paper covers the pathogenesis, clinical presentation, diagnosis and treatment of muscle cramps.