OBJECTIVE Previous reports have described prolonged paralysis after treatment with neuromuscular junction blocking agents in critically ill patients. The purpose of this study was to further describe a group of patients who developed prolonged weakness after treatment with these agents. METHODS Clinical information, electrodiagnostic and muscle pathology results are described in this group of patients. Clinical information includes diagnoses, dosage of neuromuscular junction blocker, other medications affecting the neuromuscular system, and neuromuscular examination and clinical course. METHODS All patients were seen in the ICUs of three local hospitals. METHODS Included were critically ill patients with a variety of diagnoses, all of whom developed severe weakness after discontinuation of neuromuscular junction blocking agents. METHODS Electrodiagnostic studies and muscle biopsies were performed on several of the patients. RESULTS All patients had pronounced weakness without sensory loss. Electrodiagnostic and muscle pathology findings were consistent with failed neuromuscular transmission. Although many patients had disorders or were taking medications that can injure the neuromuscular system, no disorder or medication was common to all. Recovery of strength often took several months and most patients were slow to wean from mechanical ventilator support. CONCLUSIONS Although alternative explanations cannot be excluded with certainty, the use of neuromuscular junction blocking agents may lead to neurogenic atrophy and care must be taken when using them.