The article reviews information on the epidemiology of HIV/AIDS and behavioural networking to examine the role of population mobility in spreading HIV across the Indo-Nepal border. Documents were collected through a systematic search of electronic databases and web-based information resources, and the review focuses on studies about types of the virus, prevalence of HIV, and sexual and injecting networking. HIV-1 (subtype C) and HIV-2 were identified in Nepal. The prevalence of HIV was higher among male labour migrants and female sex workers (FSWs) who returned from India, especially from Mumbai, than in similar non-migrant groups. In the early 2000s, about 6-10% of Mumbai returnee men, compared to up to 4% of India returnee men and up to 3% of non-migrant men in the far-west Nepal, were identified with HIV. Likewise, when the prevalence of HIV among sex workers in Kathmandu was found to be 17% in 1999-2000, up to 44% of India returnee and 73% of Mumbai returnee FSWs were identified with the virus. These data are, however, based on small samples with questionable representativeness of the target populations and need to be interpreted cautiously. They also generate a biased impression that HIV was coming into Nepal from India. Recently, the possibility of a two-way flow of HIV across the Indo-Nepal border through injecting and sexual networking have been indicated by serological and behavioural data from a south-eastern cluster of Nepal and a north-eastern district of India. Although similar behavioural networks exist along other segments of the border, serological data are unavailable to assess whether and how extensively this phenomenon has caused the spread of HIV. Collaborative research and interventions covering both sides of the border are desirable to fully understand and address the prospect of HIV epidemics associated with cross-border population mixing.