The population of Nigeria in 2003 was estimated by the United Nations at 124,009,000, which placed it as number 10 in population among the 193 nations of the world. It is the most populated country in Africa. In 2003 approximately 3% of the population was over 65 years of age, with another 44% of the population under 15 years of age. There were 101 males for every 100 females in the country in 2003. According to the UN, the annual population growth rate for 2000–2005 is 2.53%, with the projected population for the year 2015 at 161,726,000. The population density in 2002 was 141 per sq km (364 per sq mi). Regional differences are significant; population is densest in the south and sparsest in the north.
It was estimated by the Population Reference Bureau that 44% of the population lived in urban areas in 2001. The principal cities include Lagos, the former capital and still the largest city, with an estimated metropolitan population of 13,488,000 and the highest population density of any major African urban conglomeration. The capital city, Abuja, had a population of 403,000 in that 2003. Ibadan had a metropolitan population of 1,739,000 people, and Kano had over 1 million. According to the United Nations, the urban population growth rate for 2000– 2005 was 4.1%.
The prevalence of AIDS/HIV has had a significant impact on the population of Nigeria. The United Nations estimated that5.8% of adults between the ages of 15–49 were living with HIV/
AIDS in 2001. The AIDS epidemic causes higher death and infant mortality rates, and lowers life expectancy.