Organophosphate flame retardants (OPFRs) are an important group of pollutants associated with endocrine disorders, cancer, and nephrotoxicity. However, temporal trends in OPFR metabolite concentrations remain understudied.To examine changes in urinary concentrations of OPFR metabolites among US children, youths, and adults from 2011 to 2020, and to evaluate whether sociodemographic factors were associated with variations in temporal trends.This population-based cross-sectional study used data from 4 US National Health and Nutrition Examination Survey (NHANES) cycles (2011-2012, 2013-2014, 2015-2016, and 2017-2020 [to March 2020 before the COVID-19 pandemic]). The study included children and youths (aged 6-19 years) and adults (aged ≥20 years) with valid urinary concentrations of the following OPFR metabolites: bis(2-chloroethyl) phosphate (BCEtP), bis(1-chloro-2-propyl) phosphate (BCPP), diphenyl phosphate (DPhP), and dibutyl phosphate (DBuP). Data analysis was performed between February and May 2024.Calendar year and key sociodemographic subgroups (age, race and ethnicity, sex, educational attainment, and poverty-to-income ratio).The main outcome was urinary concentrations of OPFR metabolites among children, youths, and adults. Survey-weighted linear regression models were applied to estimate trends.The study population of 10 549 NHANES participants included 3154 children and youths (mean [SE] age, 12.5 [0.1] years; 51.2% were male) and 7395 adults (mean [SE] age, 47.8 [0.4] years; 52.0% were women). Among children and youths, mean (95% CI) BCEtP concentrations decreased from 0.68 (0.60-0.77) μg/L in 2011-2012 to 0.41 (0.37-0.45) μg/L in 2017-2020 (P for trend < .001). Among adults, mean (95% CI) BCEtP concentrations decreased from 0.43 (0.37-0.50) μg/L in 2011-2012 to 0.29 (0.27-0.33) μg/L in 2017-2020 (P for trend < .001), and mean BCPP concentrations decreased from 0.15 (0.14-0.17) μg/L to 0.13 (0.12-0.14) μg/L (P for trend = .002). Parent level of educational attainment was associated with concentrations of BCPP and BCEtP among children and youths; however, no significant differences among adults were observed.This study identified variations in temporal trends in urinary concentrations of OPFR metabolites among the US population from 2011 to 2020. In addition, substantial disparities in exposure levels persisted among children with different levels of parent educational attainment. These findings suggest that policy makers should consider socioeconomic factors to further reduce OPFR exposure and promote equity, ensuring a safe living environment for all individuals.