Nondepolarizing neuromuscular blocking agents (NMBA) are being used with increasing frequency in critically ill patients. Recently, many centers have described patients with prolonged muscle weakness after long-term use of these agents, either alone or in combination with other agents or disorders. Brief weakness lasting several hours to several days is probably the result of prolonged neuromuscular blockade, while more prolonged weakness lasting several weeks to months is, in all likelihood, caused by a myopathy. Patients with this myopathic disorder have flaccid paralysis with intact cognition and sensation. Electrodiagnostic findings include decreased M-wave amplitudes, positive waves and fibrillations, and rapid recruitment of small amplitude short duration, polyphasic motor unit potentials. Muscle biopsy findings include atrophy of type I and type II fibers, myofiber necrosis, and selective loss of thick myofilaments. The myopathy is believed to be related to the prolonged use of NMBA either alone or in combination with other disorders or medications, particularly corticosteroids. The weakness experienced by these patients leads to additional respiratory compromise, difficulty weaning from the ventilator, and prolonged hospitalization.