Clozapine is a neuroleptic drug used in selected schizophrenic patients. Its use is limited because of unpredictable myelotoxicity. The potentially dangerous interaction between cancer treatment and clozapine is virtually unknown. A 37-year-old schizophrenic patient under treatment with clozapine, diagnosed with undifferentiated nasopharyngeal carcinoma, was treated with full-dose cisplatin and concomitant radiotherapy without reporting significant neutropenia. Clozapine may be cautiously administered when full-dose concomitant chemoradiation therapy is required.