In the Peruvian North Coast (PNC), the number of Plasmodium vivax malaria cases increased steadily from 2007 to 2010 despite a significant decline in the overall number of cases in Peru during the same period. To better understand the transmission dynamics of P. vivax populations in the PNC and the neighboring Ecuadorian Amazon Basin (EAB), we studied the genetic variability and population structure of P. vivax in these areas. One hundred and twenty P. vivax isolates (58 from Piura and 37 from Tumbes in thePNCcollected from 2008 to 2010 and 25 from theEAB collected in Pastaza from 2001 to 2004) were assessed by five polymorphic microsatellite markers. Genetic variability was determined by expected heterozygosity (He) and population structure by Bayesian inference cluster analysis.Wefound very low genetic diversity in the PNC (He = 0-0.32) but high genetic diversity in the EAB (He = 0.43-0.70). Population structure analysis revealed three distinct populations in the three locations. Six of 37 (16%) isolates from Tumbes had an identical haplotype to that found in Piura, suggesting unidirectional flow from Piura to Tumbes. In addition, one haplotype from Tumbes showed similarity to a haplotype found in Pastaza, suggesting that this could be an imported case from EAB. These findings strongly suggest a minimal population flow and different levels of genetic variability between these two areas divided by the Andes Mountains. This work presents molecular markers that could be used to increase our understanding of regional malaria transmission dynamics, which has implications for the development of strategies for P. vivax control.