The presence of HIV infection in Pakistan remains concentrated in specific population known as 'key risk population' and the behaviour they exhibit increases the risk of contraction of the infection. A study conducted by the CIDA-funded Canada-Pakistan Surveillance Project shows that the presence of HIV infection remains concentrated in specific populations, key population at risk, due to behaviour they exhibit that increases their risk of contraction HIV infection. These key populations include male sex workers, female sex workers, hijras, and injecting drug users. These key populations are dependent on drug use and the men, women and transgender populations who are engaged in provision of sex as a means of their income. The Canada Pakistan HIV/ AIDS Surveillance Project (HASP) has been a critical part of the Enhanced Programme's HIV response in Pakistan from 2004 to date, and has provided timely and relevant information, by collecting serial data from key populations to describe trends in the HIV epidemic in Pakistan. The broad objective of the research was to provide accurate information on the size and characteristics of key populations IDUs, FSWs, MSWs and HSWs in 19 cities of Pakistan. The methodology was based on a geographical approach, supplemented by network mapping of female sex and hijra sex worker (HSW) networks. The risk environment is rapidly changing; sex work is getting more clandestine, dispersed and hard to reach, increasing trends of injecting among drug users. HIV prevalence during the year 2011 in Pakistan's 17 big cities including Karachi, Larkana, Sukkur, Dadu, Multan, Faisalabad, Sargodha, Lahore, DG Khan, Rawalpindi, Gujrat, Pakpattan, RYK, Peshawar, Haripur, Quetta and Turbat was recorded to be 3.1 percent among the male sex workers (MSWs), 7.3 percent among the hijras, 0.8 percent among the female sex workers (FSWs) and 36.7 percent among the Injecting drug users (IDUs). The study shows that Peshawar had the highest prevalence of HIV infection (0.22 percent) followed by Multan (0.07 percent), Karachi and Larkana. HIV infection in Peshawar can be related to migration of a large number of Afghan refugees. There is a dire need for rapid implementation of effective programmes to reduce sexual transmission among the communities. Low levels of literacy and awareness about health and HIV/AIDS, High number of at-risk population, strong sexual networks among at-risk population, highly vulnerable youth, inadequate safe blood transfusion practices, unsafe injection practices and high injection per capita are among the main factors behind the increase of the disease in Pakistan. The studies show that HIV pandemic is one of the greatest challenges that the world faces today. At the end of 2010, 34 million people were estimated to be living with the virus. There were 390,000 new infections among children under the age of 15.