The hippocampus is a key structure in feeding behaviors and weight regulation. Obesity may lead to disruptions in hippocampal structure. In animals, obesity‐related factors (e.g., high‐fat/sugar foods) are associated with hippocampal insult (e.g., alterations in the blood brain barrier). In humans, individuals with obesity, relative to healthy weight, have smaller hippocampal volumes. Few studies have examined the association between body weight and the hippocampus during adolescence, a critical brain development period. This study examined hippocampal volume and tissue signal intensity in adolescents across the weight spectrum.

Structural magnetic resonance imaging and anthropomorphic data were available for 102 12‐ to 18‐year‐old adolescents (53% female; 15.07 [SD 1.84] years; standardized BMI [BMIz] scores using the Centers for Disease Control and Prevention growth charts: 0.54 [SD 1.17]) from the Pediatric Imaging, Neurocognition, and Genetics database. Linear regression models controlling for age, sex, genetic ancestry, scanner, and household income examined the relationship between BMIz, hippocampal volume, and T2‐weighted hippocampal signal intensity.

BMIz was negatively associated with T2‐weighted hippocampal signal intensity in the left (t = −3.05; P = 0.003; r = −0.21) and right (t = −2.50; P = 0.01; r = −0.36) hippocampi. BMIz was not significantly associated with hippocampal volume.

BMIz is associated with hippocampal tissue characteristics during adolescence, which could impact later brain development.