Data on malaria transmission intensity and prevalences of asexual parasites and of gametocytes were obtained in an urban district of Yaoundé, Cameroon. The transmission level from mosquito to human was determined by indoor night capture of mosquitoes on human volunteers, revealing a calculated entomological inoculation rate of 34 infectious bites per person per year. Only Anopheles gambiae and A. funestus contributed to malaria transmission and their distribution was seasonal. Cross-sectional surveys every 2 months from July 1999 to May 2000 (n = 965) showed average annual prevalences of 35% Plasmodium falciparum asexual parasites (range 29-38%) and 4.4% gametocytes (range 0-6.7%). Prevalence of high parasitaemia (> 400 parasites/microL) and of gametocytes was seasonal. Prevalence of asexual parasitaemias and of gametocytaemias was age-dependent. The potential infectious reservoir in this area is dominated by the age group 0-15 years, representing 75% of carriers of asexual parasites (P < 0.001), 85% of carriers of high parasitaemias (P < 0.001), and 83% of gametocyte carriers (P = 0.03). Full year logistic models developed from the available data accurately predicted parasite prevalences in subsequent analyses, thus permitting a precise determination of study samples for intervention and seroepidemiology studies, and analysis of the infectious reservoir in this area.