Introduction: The present study aimed to determine the prevalence and factors associated with Giardia intestinalisinfection, verifying its impact on the nutritional status of children in northeastern Brazil. Methodology:A cross-sectional study was conducted to obtain parasitological, sociodemographic, and anthropometric data in two municipalities in the states of Piauí and Ceará, northeastern Brazil. Results: Prevalence of giardiasis was 55/511 (10.8%). G. intestinaliswas more frequent in people living in poverty (30/209 [14.4%], p = 0.041), performing open evacuation (26/173 [15%], p = 0.034), and drinking rainwater stored in cisterns (9/56 [16.1%], p = 0.005). The proportion of stunting and being underweight in children infected with G. intestinaliswas significantly higher than that in uninfected children (5/23 [21.7%] vs. 10/179 [5.6%], p = 0.017, OR = 4.69, 95% confidence interval [CI] = 1.44–15.25 and 5/23 [21.7%] vs. 13/179 [7.3%], p = 0.038, OR = 3.54, 95% CI = 1.13–11.09, respectively). Infection with G. intestinalisremained significantly associated with stunting and being underweight after adjustment for poverty, municipality, sex, and age in a logistic regression multivariate model. Conclusions: In rural areas in northeastern Brazil, giardiasis has acquired great public health importance in the soil-transmitted helminths control era, impacting the nutritional status of children and requiring new approaches to diagnosis and treatment and translational research that could generate applicable solutions at the community level.