Less than 1% of adult patients with schizophrenia taking clozapine develop agranulocytosis, and most of these cases occur within the first weeks of treatment. The human leukocyte antigen (HLA) region has been associated with genetic susceptibility to clozapine-induced agranulocytosis (single amino acid changes in HLA-DQB1 (126Q) and HLA-B (158T)). The current study aimed to evaluate the cost-effectiveness, from a healthcare provider's perspective, of an HLA genotype-guided approach in patients with treatment-resistant schizophrenia who were taking clozapine and to compare the results with the current absolute neutrophil count monitoring (ANCM) schemes used in the USA. A semi-Markovian model was developed to simulate the progress of a cohort of adult men and women who received clozapine as a third-line antipsychotic medication. We compared current practices using two genotype-guided strategies: (1) HLA genotyping followed by clozapine, with ANCM only for patients who tested positive for one or both alleles (genotype-guided blood sampling); (2) HLA genotyping followed by clozapine for low-risk patients and alternative antipsychotics for patients who tested positive (clozapine substitution scheme). Up to a decision threshold of $3.9 million per quality-adjusted life-year (90-fold the US gross domestic product per capita), the base-case results indicate that compared with current ANCM, genotype-guided blood sampling prior to clozapine initiation appeared cost-effective for targeted blood monitoring only in patients with HLA susceptibility alleles. Sensitivity analysis demonstrated that at a cost of genotype testing of up to USD700, HLA genotype-guided blood monitoring remained a cost-effective strategy compared with either current ANCM or clozapine substitution.