Occupational "horizontal segregation," defined as disparity in the distribution of responsibilities between genders, could discourage women from seeking careers in radiology, as well as impact women within radiology in terms of compensation, promotion, and career advancement. We aimed to explore the existence of horizontal workplace segregation in radiology, as potentially manifested as intergender differences in the distribution of clinical work effort among imaging modalities for radiologists.Medicare-participating general radiologists, neuroradiologists, abdominal, cardiothoracic, and musculoskeletal radiologists were identified from the 2016 Medicare Physician and Other Supplier Public Use File. Work effort in radiography, ultrasound, CT, and MRI was stratified by gender. Univariable and multivariable analyses were performed.22,445 radiologists were included (19.0% female; 19.6% in academic practices). At univariable analysis, female (vs. male) generalists had lower work effort in MRI (10.2% vs. 13.2%) (p < 0.001); abdominal radiologists had higher work effort in ultrasound (27.1% vs. 21.9%), with lower work effort in CT (53.7%. vs. 56.0%) and MRI (8.1%. vs. 9.4%) (p < 0.001); and musculoskeletal radiologists had higher work effort in radiography (41.6% vs. 34.8%) and less in MRI (44.8% vs. 49.6%) (p = 0.007). In multivariable analyses, female gender was independently associated with lower work effort in advanced imaging (CT and MRI) for generalists (coefficient, -0.020; p < 0.001), abdominal radiologists (coefficient, -0.042; p < 0.001), and neuroradiologists (coefficient -0.010; p = 0.035).Horizontal occupational segregation exists in radiology with female radiologists devoting lower work effort to advanced imaging modalities. Further investigation is warranted to better understand the sources and downstream implications of such variation.