Background: In India, currently 2.1 million people are living with HIV. Prevention is the mainstay of the strategic response to HIV/AIDS in India. Awareness rising brings behaviour change. People inhabiting slums have low awareness and are more vulnerable to RTI/STIs and HIV/AIDS. Aims: To assess HIV/AIDS knowledge, sexual behaviour, reported symptoms of STI/RTI’s along with the socio demographic profile of adult population of urban slum dwellers. Methods: A cross sectional, qualitative study. The study area, chosen by convenience sampling was an urban slum located in M East Ward of Greater Mumbai. The study was finally conducted with 104 participants. Results: The mean age of surveyed participants was 23.5yrs and nearly 38(40%) of participants were illiterate Age at first sexual intercourse among the study participants was between 12-16 years for 23(22.10%) participants. Among study participants; 30(29%) of participants do not have any knowledge about prevention and transmission of HIV/AIDS. Conclusions: Urban slum residents in Mumbai have knowledge gap regarding HIV/AIDS transmission and prevention. Initiation of sexual intercourse is at an early age, a high percentage report symptoms of STI/RTIs.