India has the world's highest number of HIV/AIDS infections for any country outside Africa. Eighty-five per cent of HIV transmission in India occurs through heterosexual contact. One billion population, a large number of female sex workers, high prevalence of sexually transmitted infection (STIs) and low condom use make a potent combination for explosive growth of the epidemic. Taking available estimates of the number of female sex workers (FSWs), their work patterns, prevalence of HIV and STIs and condom use among them in 1999 as the base, and adopting reasonable infectivity rates, this paper attempts to present a model to estimate the spread of HIV infection in commercial sex networks until 2005. HIV infections in commercial sex networks are estimated to increase from the 1999 level of approximately 2.49 million to about 3.93 million by 2005 in a favourable scenario, and to 6.87 million in a worse scenario. Spread of HIV is influenced in the short term by condom use and prevalence of STIs, and these are the only factors that can be manipulated to limit the spread of the infection.