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The use of clozapine, which is an atypical antipsychotic known for its superior efficacy for refractory schizophrenia, is especially challenging for clinicians, when patient has a medical condition that could also cause hematological complications. There is no guideline information for clozapine use in the presence of ongoing or past blood dyscrasia history or during cancer chemotherapy. Following case draws attention regarding the management of a patient with schizophrenia stabilised on clozapine but who also suffers from a different reason of agranulocytosis other than the known adverse effect of clozapine. A 53-year-old patient with resistant schizophrenia, who had been on several antipsychotic regimens before and has been stable since 1997 after the introduction of 600mg/day clozapine. In 2005, he was diagnosed to have chronic lymphocytic leukemia and chemotherapy was started. We continued both clozapine treatment and chemotherapy until 2012, when he developed neutropenia. After discontinuing clozapine treatment, he started to have delusions and agitation despite 8mg/day risperidone. With the consent of relatives and hematological team, we decided to reintroduce clozapine. His mental status has been stable since then and white blood cell count has not decreased. There are only a few case reports published clozapine use during chemotherapy. To make a decision whether stop or continue clozapine during cancer chemotherapy has always been a challenge. Although there is no consensus about mechanism of clozapine induced agranulocytosis, it seems it can be best explained by genetic and immunotoxic factors. This theory led us to the idea of continuing clozapine therapy during chemotherapy can relatively be a safe treatment method for patients already stabilised on clozapine.