There is an ongoing challenge of promoting HIV testing uptake and sustained treatment adherence among key and vulnerable populations. This study aimed to determine the characteristics and perspectives of HIV-positive individuals among the key and vulnerable populations in Surabaya, Indonesia. This was a cross-sectional study with a mixed-methods in HIV-positive key and vulnerable populations. Clinical and laboratory data were obtained from medical records. A questionnaire collected data on sociodemographic characteristics, behavior, sexual practices, cognitive function, depression, and quality of life. The study indicated that 52.8% of participants were HIV-late diagnosis with several characteristics: being male (p=0.021); having lower BMI (p=0.001), lower lymphocyte count (p<0.001), poor knowledge of HIV cause (p=0.016), low quality of life on physical health (p<0.001), psychological health (p=0.020), and social relationship (p<0.001); lower cognitive function (p<0.001); and moderate to severe depression (p<0.001) than non-HIV late diagnosis. The interviews revealed that most participants hid their HIV status from their families and experienced stigma. NGO staff played a crucial role in educating, encouraging, and assisting them in accessing relevant health services. More than half of the participants were diagnosed late. Improving community-based programs, expanding mental health resources, and reducing stigma are the key strategies for enhancing HIV-related outcomes.