© 2014 Taylor Francis. The Centers for Disease Control and Prevention recommends routine human immunodeficiency virus (HIV) testing of every client presenting for services in venues where HIV prevalence is high. Because older adults (aged ≥50 years) have particularly poor prognosis if they receive their diagnosis late in the course of HIV disease, any screening provided to younger adults in these venues should also be provided to older adults. We examined aging-related disparities in recent (past 12 months) and ever HIV testing in a probability sample of at-risk adults (N = 1238) seeking services in needle exchange sites, sexually transmitted disease clinics, and Latino community clinics that provide HIV testing. Using multiple logistic regression with generalized estimating equations, we estimated associations between age category (<50 years vs. ≥50 years) and each HIV testing outcome. Even after controlling for covariates such as recent injection drug use, older adults had 40% lower odds than younger adults did of having tested in the past 12 months (odds ratio [OR] = 0.6; 95% confidence interval [CI] = 0.40-0.90) or ever (OR = 0.6; 95% CI = 0.40-0.90). Aging-related disparities in HIV testing exist among clients of these high HIV prevalence venues and may contribute to known aging-related disparities in late diagnosis of HIV infection and poor long-term prognosis.