Five generally healthy women who had complaints related to their Norplant contraceptive implants were given medical, psychiatric, and neurologic examinations including mental status, cranial nerve, cerebellar, sensory, and reflex assessments. When indicated, electrical neurophysiological, olfactory, and additional neurologic and psychiatric tests were done. After taking potentially confounding variables into account, 4 of the 5 subjects met criteria for clinical diagnoses of Norplant-induced neurotoxicity, with 0 to 4 clinical diagnoses per subject (mean 2 per subject) as follows: Norplant-induced encephalopathy, 1 subject; Norplant-induced limbic encephalopathy, 2 subjects; Norplant-induced cephalgia, 4 subjects; Norplant-induced polyneuropathy, 1 subject; Norplant-induced autonomic neuropathy, 1 subject. In addition, subclinical diagnoses were made as follows: Norplant-induced encephalopathy, 2 subjects; Norplant-induced polyneuropathy, 1 subject; Norplant-induced autonomic neuropathy, 2 subjects. Given the widespread use of this birth-control device, these results indicate a potentially major public health problem. Evaluation of a larger sample of Norplant users is recommended to provide statistical significance.