We have previously shown that antibody responses directed to Plasmodium falciparum merozoite surface protein (MSP)-1, MSP-2 and glutamate-rich protein (GLURP) are associated with anti-malarial protection in residents of the Niakhar area of Senegal. In the same area, urinary schistosomiasis is frequent and we therefore assessed the possible influence of Schistosoma haematobium infection on these protective anti-malarial IgG responses. After adjustment for confounders, we found that the levels of IgG1 directed to MSP1 and GLURP were significantly lower in helminth carriers. The higher circulating levels of interleukin (IL)-10 present in the plasma of co-infected individuals were associated with decreased anti-plasmodial IgG responses, particularly of those directed to MSP-2. Our data thus reveal a modulation of P. falciparum-specific immune responses in the presence of a trematode helminth infection, potentially increasing infected individuals' risk of plasmodial infection or disease.