Muscle cramps may occur in healthy individuals without any apparent cause; these are regarded as benign cramps. Cramps may also develop as a symptom of a systemic disease, such as uremia. Cramps probably originate in the distal portion of the motor nerve. It is unclear whether the nerve terminals are hyperexcitable or prone to repetitive activity in the various related conditions. In the cancer patient, muscle cramps may not be a benign complaint because they often represent an unsuspected underlying pathologic condition associated either with the neoplastic process or the undesirable side effects of therapy. Initial evaluation with a detailed neurologic examination, a complete biochemical profile with magnesium levels and muscle enzymes, and electrodiagnostic examination will lead to the diagnosis in the majority of these patients. Recognized etiologies of cramps may be related to neurologic abnormalities or to nonneurologic causes. Treatment decisions should be oriented according to the following classification: (1) reversible causes; (2) potentially reversible causes and (3) irreversible causes. Whereas the remedy in the first category is to attack the underlying process, if possible, pharmacologic suppression of cramps is the primary approach in the others. Membrane-stabilizing agents, such as quinine, phenytoin or carbamazepine, may be selected according to either nocturnal or daytime predominant occurrence of cramps.