Data repeatedly demonstrate that HIV-infected people who regularly utilize primary health care services are more likely to have access to lifesaving treatments (including antiretroviral medications); have better indicators of health status; survive longer; and use acute care services far less. Women tend to have poorer HIV outcomes than men, which is likely due to gender disparities in optimal utilization of HIV primary care services. To understand the relationship between gender and the HIV health care system, we collected interview and medical record data between August 12, 2004 and June 7, 2005 from 414 severely marginalized, HIV-infected people in New York City and examined whether gender-related disparities in HIV health care utilization existed, and, if so, whether these patterns were explained by patient sociodemographic=behavioral characteristics and=or attitudes toward the health care system and providers. Women were significantly less likely to have optimal HIV health care services utilization, including lower use of HIV primary care services (odds ratio [OR] ¼ 0.56, 95% confidence interval [CI] ¼ 0.35, 0.90) and greater use of the emergency department (OR ¼ 2.13, 95% CI ¼ 1.31, 3.46). Although we identified several factors associated with suboptimal HIV health care services utilization patterns in addition to female gender (low education, insurance status, mistrust of the health care system, and poor trust in health care providers), we were unable to identify factors that explained the observed gender disparities. We conclude that gender disparities in HIV health care utilization are due to a complex array of factors, which require more qualitative and quantitative research attention. Development of intervention strategies that specifically target severely disadvantaged women's HIV health care utilization is in great need.