Objectives Mental health (MH) care for people living with HIV (PLWH) emerges as an important unmet need, yet there are no integrated HIV-MH clinics in Turkey. Our aim is to determine MH service use and its associated factors in PLWH followed up in the HIV/AIDS outpatient clinics in Istanbul/Turkey. Methods A cross-sectional study was conducted at the HIV/AIDS outpatient clinics of the Infectious Diseases (ID) departments in hospitals affiliated with the ACTHIV-IST Study Group. Structured interviews were performed using questionnaires that covered psychiatric state, medical history, and help-seeking behavior. Results Out of 172 outpatients, 121 (70.3%) reported MH complaints after infection, and 65.6% felt a need to see MH professionals. Among those, 59% shared their MH distress with the ID team. However, only 20.7% applied to an MH service, and 16.5% received psychiatric treatment. Previous MH diagnoses (AOR = 4.11; 95%CI = 1.26–13.39), sharing the disease with the ID team (AOR = 4.18; 95%CI = 1.24–14.11), and being hospitalized due to HIV (AOR = 6.54; 95%CI = 1.21–35.39) emerged as the predictors of MH service use among those who would like to see an MH professional in logistic regression. Conclusions Closer contact with the healthcare system may increase the chances of PLWH receiving MH care. Thus, integrating MH services in HIV/AIDS care would help reach more PLWH who are distressed.