Health anxiety is a condition which can negatively impact the well-being of an individual through rumination or extreme safety measures. However, literature about the factors related to adolescent health anxiety is scarce. In this study, we explored factors potentially related to adolescent health anxiety. Using structural equation modeling, we analyzed data from 1530 Czech adolescents aged 13–18, recruited through quota sampling, and their caregivers (64% female). First, we focused on its transmission from caregiver to offspring and on the moderating effect of gender. Second, we studied the relationship between online health information seeking and adolescent health anxiety with eHealth literacy as a potential moderator. The responses partially supported our hypotheses. Adolescent health anxiety was positively related to the health anxiety of the caregiver. Disease information seeking was positively related to health anxiety, but we found no such effect for fitness information seeking. Finally, eHealth literacy did not moderate online health information seeking. Our results underline that the health anxiety of caregivers and their offspring are intertwined and should ideally be addressed together. Furthermore, we show that for adolescents, like adults, online disease information seeking can be related to health anxiety and should be considered.