Reduced deformability of both infected and uninfected red blood cells (RBCs) contributes to pathogenesis in Plasmodium falciparum malaria. Whole-blood RBC deformability (RBC-D) is not well characterized in Plasmodium vivax malaria. We used a laser-assisted optical rotational cell analyzer to measure the RBC-D in fresh whole-blood samples from Malaysian patients with vivax malaria (n = 25). Deformability of whole-blood RBCs, the vast majority of which were uninfected, was reduced in vivax malaria compared with controls (n = 15), though not to the same degree as in falciparum malaria (n = 90). Reduced RBC-D may contribute to the pathogenesis of vivax malaria, including splenic retention of uninfected RBCs.