Mr. A, a 28-year-old Caucasian man with AIDS, came to the emergency department after 2 weeks of worsening mania with an elevated mood, increased energy, decreased sleep, increased activity, racing thoughts, grandiose delusions, and auditory hallucinations. Approximately 1 month earlier, he was prescribed the testosterone patch for a 20-lb weight loss occurring over the previous 2 years. Mr. A had a history of bipolar II disorder (DSM-IV) but had never previously become psychotic or required hospitalization. A medical workup excluded infection or other AIDS-related processes as the cause of his psychosis. He was started on a regimen of divalproex, 500 mg/b.i.d., and his usual anti-AIDS regimen was continued, except for the testosterone patch. By day three, his sleep and energy had improved, but his psychosis and racing thoughts persisted. A regimen of risperidone, 4 mg at bedtime, was added with good results. Because he had a history of idiopathic thrombocytopenic purpura, his dose of divalproex was discontinued on the fourth day when his platelet count dropped from 100,000 to 65,000. Although Mr. A refused to take another mood stabilizer, he remained much improved and was discharged on a regimen of risperidone monotherapy.