The inherent risk of agranulocytosis associated with clozapine requires the realization of weekly white blood cell monitoring (WBCM) during the 18 first weeks of treatment. The aim of this study was to assess the compliance with WBCM during clozapine initiation for schizophrenia and Parkinson's disease (PD) subjects. The analysis was conducted using SNDS data on a cohort of new users of clozapine in 2018. We analyzed all reimbursements for WBCM from 2 weeks before the index date to 18 weeks after (optimal monitoring during hospitalization was assumed). The primary outcome was the proportion of good realization of WBCM according to different thresholds of completion (70%; 80%; 90%). Descriptive and comparative analyses with chi-squared test or Student's t-test were performed. Two hundred and ninety-six subjects were included. Rates of patients with WBCM realization over 70%, 80%, and 90% of WBCM expected were, respectively, 78.1%, 70.0%, and 56.9% for subjects with schizophrenia and 71.3%, 63.2%, and 47.8% for PD subjects. Only hospitalization during the follow-up period for schizophrenia subjects was significantly associated with good WBCM realization. We observed rather good results for compliance with clozapine initial monitoring. Other studies are needed to confirm our results.