OBJECTIVE We evaluated Illinois and Chicago Departments of Public Health surveillance databases to determine risk factors associated with newly diagnosed HIV among persons with bacterial sexually transmitted diseases (STDs). METHODS Test results for Chlamydia, gonorrhea, early syphilis (primary, secondary, and early latent), and HIV from public health clinics in Illinois in 2002 were merged with demographic and behavioral survey data collected during patient visits. STD was defined as any positive non-HIV result. RESULTS Among 43,517 patient encounters, 5814 (13.4%) had positive STD test results. There were 308 (0.7%) positive new HIV test results, of which 71 (23.1%) had concomitant infection with an STD. Compared with STD-positive, HIV-negative cases, age >30 years (OR = 1.9, 95% CI, 1.0,4.4), men who have sex with men (MSM) (OR = 22.2, 95% CI 11.3-43.7), and bisexual male (OR = 22.4, 95% CI 7.8-64.8) were independently associated with STD and HIV coinfections. Among distinct STDs, syphilis (n = 438) was the least frequent (7.5%), but was reported in the highest proportion (10.1%) of all new HIV infections and conferred the greatest risk (OR = 11.0, 95% CI 7.7-15.8) for newly diagnosed HIV. CONCLUSIONS MSM were at increased risk for newly diagnosed HIV with STD coinfection. Persons with a concomitant STD and HIV were older than US populations that generally constitute the greatest proportion of STD cases. These results highlight the role in particular of syphilis among populations at high risk for HIV transmission. Public health interventions targeting MSM and older adults for effective testing and prevention strategies are critically needed within high-risk networks for cotransmission of STDs and HIV.