Thionamides are anti-thyroid drugs (ATD) used to treat autonomous thyrotoxicosis. Although efficacious, these medications carry a risk of neutropenia or agranulocytosis. Some risk factors for ATD-induced neutropenia have been identified, including dose, age, and female sex, but the role of race and ethnicity has not been well studied. We hypothesize that there will be no effect of race or ethnicity on the change in Absolute Neutrophil Count (ANC) following initiation of ATD therapy. Data from the Electronic Medical Record at UNM HSC were obtained using a standard database query. Inclusion criteria were the prescription of an ATD, an ANC recorded within 30 days of initiating ATD therapy (Pre-ATD), and an ANC recorded 75 - 365 days after starting an ANC (Post-ATD). Patients taking other agents known to cause neutropenia were excluded. Racial and ethnic groups were assigned as follows: Hispanic, Non-Hispanic White, Native American, Black/African American, and Asian/Pacific Islander. Post-ATD ANC was defined as the nadir ANC after ATD initiation. "Delta ANC" was defined as ((Post-ATD ANC) - (Pre-ATD ANC)). ANOVA analysis with Bonferroni-adjusted post-hoc testing and multiple regression were performed to examine differences in the mean changes in ANC across ethnic groups. One hundred and twenty-three adult patients met inclusion and exclusion criteria and were included in the analysis. The Native American group showed a significantly greater Post-ATD ANC and Delta-ANC as compared to the other groups (p<0.001). In this cohort of New Mexicans with thyrotoxicosis, Native American race was protective against thionamide-induced neutropenia.