Inhalant toxicants are postulated to contribute to the pathogenesis of chronic rhinosinusitis. Permethrin is a pesticide widely used in agricultural, industrial, and residential settings. The objective of this pilot study is to investigate the in vitro effects of permethrin on sinonasal epithelial cells (SNECs). Sinus mucosa was collected from 4 patients undergoing transsphenoidal pituitary surgery without a history of chronic rhinosinusitis. Cultured SNECs were exposed to varied concentrations of permethrin (0-156 µM) for 6 days. Cell viability and proliferation were determined via the MTT colorimetric assay and the Incucyte Live Cell Imaging System. Cellular reactive oxygen species (ROS) activity was measured by the DCFDA ROS detection assay. A statistically significant reduction in cell viability and proliferation was observed between the exposure and control groups at certain concentrations, and a dose-dependent increase in ROS activity was also observed. These findings indicate that permethrin may have deleterious effects on SNECs in a dose-dependent manner.