A 55-year-old man had schizophrenia with acute exacerbation, without history of major surgery, hematologic disorder, or drug abuse. He was admitted for disorganized speech, auditory hallucinations, and persecutory delusions. Initial laboratory studies, including thyroid function test, and serum electrolyte, were within normal range. The white blood count (WBC) was 5,100 cells/mm3. Initially, quetiapine 1,200 mg was prescribed for 1 month. Because of inadequate control of symptoms and unacceptable sedative effect, quetiapine was tapered and stopped within 1 week, and risperidone 6 mg was added. One week later, all laboratory results were normal except the WBC and ANC. His WBC and ANC were 2,800 cells/mm3 and 1,400 cells/mm3, respectively, in the afternoon. Physical examination revealed no infectious signs. Risperidone-induced neutropenia was strongly suspected, and risperidone was tapered and stopped. Aripiprazole was cross-titrated to 15 mg per day for control of his psychotic symptoms. Two weeks later, the WBC was 4,600 cells/mm3, and the ANC was 3,420 cells/mm3; and 1 month later, the WBC was 8,200 cells/mm3, whereas the ANC was 5,000 cells/mm3.