Summary

Risperidone, an atypical antipsychotic drug, is associated with neutropenia in some individuals. When the absolute neutrophil count falls below 1.8×10⁹/l clinicians may consider switching the drug. We report the case of a young man who developed neutropenia while on risperidone and also showed a pronounced diurnal variation, with normal neutrophil counts later in the day. Hence neutrophil counts should be measured in the afternoon sample before making modifications to the therapeutic agent based only on a early morning sample.