The authors applied a time-series approach to assess the temporal trend of racial disparity in chlamydia prevalence between young, socioeconomically disadvantaged blacks and whites entering the US National Job Training Program. Racial disparity was defined as the arithmetic difference between age group-, specimen type-, and region of residence-standardized chlamydia prevalences in blacks and whites. A regression with autoregressive moving average errors model was employed to adjust for serial correlation. Data from 46,849 women (2006-2008) and 136,892 men (2004-2008) were analyzed. Racial disparity significantly decreased among women (by an average of 0.122% per 2-month interval; P < 0.05) but not among men (-0.010%, P = 0.57). Chlamydia prevalence significantly declined for black women (-0.139% per 2-month interval; P = 0.004), black men (-0.045%, P < 0.001), and white men (-0.035%, P = 0.002) but not for white women (-0.028%, P = 0.413). Despite the decreases among black women and black men, the black-white disparities remained high for both sexes; in 2008, the racial disparity was 8.1% (95% confidence interval: 6.8, 9.3) for women and 9.0% (95% confidence interval: 8.4, 9.6) for men. These findings suggest that current chlamydia control efforts may be reaching young black men and women but need to be scaled up or modified to address the excess risk among blacks.