In adults, paranasal sinus agenesis is an uncommon anomaly that appears mainly in the frontal sinus. The aim of this study was to investigate the prevalence of agenesis of the frontal sinus using computed tomography in a population of Iranian individuals. Computed tomographic scans in the axial and coronal planes of the frontal sinus of 565 patients were examined for evidence of the absence of the frontal sinus. A bilateral agenesis of the frontal sinus was seen in 8.32% of cases, and unilateral absence of the frontal sinus was observed in 5.66%. The information provided in the current study is useful for some craniofacial surgeries and improves the anthropometric knowledge of humanity. There are limited studies on agenesis of the frontal sinus in the literature, but comparing our findings with the available data, there were differences regarding the incidence of this condition. This may be related to geographic and racial features. More studies on other population are required.