Nerd-genius stereotypes about people in the physical sciences, technology, engineering, and mathematics (pSTEM) are barriers to getting many adolescent girls interested in pSTEM. Endorsing these stereotypes may undermine youths' pSTEM identity especially when they are incongruent with their self-concepts--possibly more likely for girls than boys. Conversely, pSTEM identity may strengthen when stereotypes are congruent--possibly more for boys than girls. We tested these premises among 310 adolescents. Novel contributions of the study include the separate evaluation of youths' endorsement of four stereotypes about persons in pSTEM (geniuses, awkward, unattractive, unsuccessful at dating) and the separate consideration of two facets of self-concepts (competence and importance) in each stereotyped domain. Factor analyses confirmed the four-factor structure for self-concepts but indicated a two-factor structure for stereotypes (nerd [awkward, unattractive, unsuccessful at dating] and genius). Students' pSTEM identity was based on their felt typicality with persons in pSTEM fields. Our results generally confirmed our hypothesized model for self-perceived competence but not for importance. Congruence predicted higher pSTEM identity. Conversely, incongruence predicted lower pSTEM identity.