Background
Severe health anxiety (HA) is characterized by excessive and impairing worry and preoccupation with health issues and can cause increased and unnecessary medical examinations. HA in childhood and adolescence is scarcely explored, hindering the potential for prevention and early intervention.

Methods
HA was assessed in 1,278 children/youths at two time points at ages 11 and 16 years in a general population-based birth cohort. Register-based data on costs related to nonhospital-based primary and secondary somatic health services were obtained over the follow-up period. The presence of functional somatic symptoms, emotional disorders and chronic somatic illness at baseline were included as covariates.

Results
High HA (top 10% score) at age 11 predicted high HA at age 16 (relative risk [RR] 2.03, 95% CI: 1.26–3.31). The group with persistent HA was small (n = 17, 1.3%), resulting in broad confidence intervals. The statistical effect of HA at age 11 on HA at age 16 was heavily reduced after adjustment for sex and all covariates (RR: 1.49, 95% CI: 0.85–2.60). In the adjusted model, somatic illness at age 11 (RR: 1.91, 95% CI: 1.22–2.98) and female sex (RR: 3.33, 95% CI: 2.01–5.50) were independently associated with HA at age 16. Persistent HA was associated with approximately doubled healthcare costs compared to the group with consistently low HA. Incident HA at age 16 was associated with increased costs over follow-up. The increased costs were not explained by chronic somatic illness.

Conclusions
A small subgroup of children had persistent high levels of HA from late childhood to adolescence and displayed increased healthcare costs. Female sex and chronic somatic disorders at age 11 were independent risk factors of HA at age 16. These findings provide potential means of early identification and of therapeutic levers. Further intervention development and evaluation are needed.