Between 1995 and 1998, a longitudinal study was conducted at 2 health centers in Cameroon to determine the prevalence of Plasmodium falciparum infection in pregnant women. There were 520 pregnant women enrolled at a rural clinic in the village of Etoa and 199 enrolled at the Biyem Assi Clinic in the city of Yaounde. In Etoa, pregnant women were younger, fewer took prophylaxis, and malaria prevalence was higher compared with pregnant women in the Biyem Assi Clinic. The prevalence of malaria infection peaked during the fourth month of pregnancy at both sites. Age was identified as a major risk factor because women < or = 20 years old were 1.8 and 3.4 times more likely to have malaria infection than women > 20 years old at Etoa and the Biyem Assi Clinic after adjusting for gravidae and other factors. The use of chemoprophylaxis and seasonality did not have a major effect.