Clozapine is an atypical antipsychotic indicated for treating patients resistant to antipsychotic therapy when other medications in this class have no therapeutic effect. Clozapine has greater efficacy but more side effects than other atypical antipsychotics (e.g., agranulocytosis, seizures, sedation, and weight gain). Side effects can cause discomfort to patients and can affect patient compliance, interfering with therapeutical outcomes. This study aims to identify the side effects of clozapine use in patients at the Psychiatric Hospital Grhasia, in Yogyakarta, Indonesia. Using a cross-sectional design, this research provides a retrospective descriptive analysis using medical records of patients at the Psychiatric Hospital Ghrasia Yogyakarta. Inpatient and outpatient medical records of patients who had received a clozapine prescription from January to December 2019 were analyzed. In the 336 patients that met the inclusion criteria, the incidence of side effects from clozapine use was 16.07% (95%, CI:2.2-4.1), with the most frequent being dizziness, vomiting, diarrhea, and hypersalivation. There was no effect of age, gender, profession, or patient's disease on their incidence. The management of side effects is classified into three aspects: the drug is stopped, the patient is given additional therapy, and the patient is not given therapy. The results showed that the use of clozapine at the Psychiatric Hospital Ghrasia Yogyakarta was relatively safe. Identification of side effects is necessary to determine the follow-up treatment.