Importance The inflammation-modulating properties of sex hormones provide a pathophysiological basis for anticipating sex-based differences in chronic rhinosinusitis (CRS), but the role of biological sex has not been thoroughly studied. Objectives To investigate sex differences in CRS diagnosis and biomarkers. Design, Setting, and Participants This cross-sectional study used data from the All of Us Research Program, a large national dataset of US adults, collected from partner health care organizations including academic medical centers, Veterans Affairs facilities, and community health centers. From May 2018 to October 2023, a total of 393 596 participants with electronic health records were considered for inclusion; those with incomplete data were excluded. Data analysis was conducted from April to September 2025. Exposures Participant sex was the primary exposure, and covariates included demographics, socioeconomic status, risk factors, and comorbidities. Main Outcomes and Measures CRS diagnosis, stratified into CRS with nasal polyps (CRSwNP) and without nasal polyps (CRSsNP), and CRS biomarkers. Results The analysis included 258 245 participants, of whom 38.4% were male and 61.6% were female and most (57.3%) were 50 years or older. After controlling for covariates, female sex was associated with an increased odds of CRSsNP among those younger than 60 years (odds ratio [OR], 1.44; CI with Holm-Bonferroni correction [CIH-B], 1.35 to 1.54) and 60 years or older (OR, 1.32; CIH-B, 1.23 to 1.40), but a lower odds of CRSwNP (OR, 0.63; CIH-B, 0.52-0.76) compared to males. Compared to male participants, female participants had a lower concentration of serum eosinophils (β, −0.35; CIH-B, −0.44 to –0.25) and IgE (β, −99.73; CIH-B, −190.49 to –8.96) among participants with CRSsNP after controlling for covariates, as well as lower eosinophils among participants with CRSwNP (β, −0.41; CIH-B, −0.80 to –0.01). Analyzing CRS prevalence by age group revealed a downtrend among female participants 60 years or older, despite an upward trend at younger age groups, with regression analysis demonstrating a negative interaction effect between female sex and age 60 years or older with odds of CRSsNP (OR, 0.91; CIH-B, 0.84 to 0.99). Conclusions and Relevance This cross-sectional study found that female sex was associated with a higher odds of CRSsNP, but a lower odds of CRSwNP compared to males. Biomarker analysis indicated a possible female disposition for nontype 2 inflammation.