Rates of reported cases of chlamydia, a sexually transmitted infection, are high among adolescent women in the United States, in particular non-Hispanic black teens. Fewer than half of female teens have ever had sex and are not at risk. We adjusted national chlamydia case rates for sexual behaviour and examined differences in adjusted rates by race. We used chlamydia case data reported to CDC, census population counts, and data from the 2002, 2006–2010, and 2011–2013 National Survey of Family Growth to calculate the adjusted rates for those who have had sex (sexually experienced) and rates for those who had sex in the past year (sexually active) across race groups for female teenagers. Overall, the rates of chlamydia are higher when adjusted for sexual behaviour. The disparity in female rates for blacks relative to whites is reduced when adjusted for sexual behaviour. For example, in 2006–2008, the black to white chlamydia rate ratio decreased from 6.7 to 3.0 after adjusting for sexual experience. From 2002–2013, decreases in female black/white disparities were more pronounced after adjusting for behaviour: 6.4 to 5.3 (crude) vs. 5.1 to 3.5 (adjusted for sexual experience) and 5.9 to 3.5 (adjusted for sexual activity). From 2002–2013, the female Hispanic to white rate ratio also decreased, but was less affected by adjustment for sexual activity: 2.1 to 1.4 (crude) vs. 2.5 to 1.5 (adjusted for sexual experience) vs. 2.7 to 1.7 (adjusted for sexual activity). The impact of adjustments can be attributed to: decrease in proportion of sexually experienced/active blacks; increase in proportion of sexually experienced/active Hispanics; and stable proportion in whites. Adjustments for sexual behaviour attenuate the chlamydia rate disparity between blacks and whites, and not adjusting for behaviour underestimates the reduction in disparities over time. Black teens remain disproportionately burdened by chlamydial infections.