Although Isaacs syndrome is known by several names including neuromyotonia and quantal squander, it bears some resemblence to other syndromes characterized by muscular stiffness such as stiff-man syndrome. The purpose of this paper is to examine pertinent clinical findings about Isaacs syndrome. A patient who presented cramping pain in both thighs and difficulty releasing his grip is described. Physical examination revealed myokymia in all four extremities, hyporeflexia, and hypertrophy of the thenar musculature. Electromyographic studied show continuous motor unit activity at rest. The patient was treated with phenytoin and showed almost complete symptom resolution over a 24-hour period. Clinical and electromyographic examinations in conjunction with the rapid response to phenytoin are diagnostic characteristics of Isaacs syndrome.