[': Injecting drug use is increasing in Afghanistan but little is known about sexual risk behaviors and sexually transmitted infection (STI) prevalence among injection drug users (IDU). The purpose of this study is to assess prevalence and correlates of syphilis and condom use with female sex workers (FSWs) among male IDUs in Hirat, Jalalabad, Kabul, and Mazar-i-Sharif, Afghanistan.', ': Participants in this cross-sectional study completed an interviewer-administered questionnaire and serologic testing for syphilis between June 2005 and January 2008. Factors associated with syphilis condom use with FSWs were assessed with site-controlled logistic regression analysis.', ': Of 1078 male IDUs, most (90.3%) reported prior sexual experience, of whom 27.6% reported any condom use. Sexual experiences with FSWs (58.1%) and men or boys (25.7%) were common, although prior condom use with FSWs (32.6%) or male partners (10.8%) was relatively rare. Few reported having a lifetime STI diagnosis (6.3%, n = 68) or symptoms (10.4%, n = 110) in the last 6 months. Prevalence of syphilis was 3.72% (95% CI: 2.66%-5.06%) and varied significantly between sites ranging from 0% (Jalalabad) to 13.9% (Mazar-i-Sharif) (P < 0.001)). Syphilis was significantly associated with STI diagnosis (adjusted odds ratio [AOR] = 3.84) or sex with FSWs (AOR = 3.82) in the last 6 months, and with lower (≤6 years) educational level (AOR = 2.20). Prior condom use with FSWs was independently associated with living outside Afghanistan in the last decade (AOR = 5.52, 95% CI: 1.83-16.71), higher income (AOR = 2.03, 95% CI: 1.17-3.51), greater number of lifetime partners (AOR = 1.80, 95% CI: 1.32-2.45), and younger age (AOR = 0.985, 95% CI: 0.973-0.998).'] Does prevalence and correlate of syphilis and condom use among male injection drug users in four Afghan cities?