Objectives: 1) Estimate the prevalence of chronic disabling fatigue at age 13, and 2) investigate associations with early family adversity, using a population-based birth cohort study.

Methods: The subjects were 10,001 children, of whom 5657 had sufficient data to define chronic disabling fatigue at age 13. Chronic disabling fatigue was defined as tiredness reported by mothers that had lasted for ≥ 3 months or ≥ 6 months, was disabling (school absence or prevented participation in hobbies/sport/leisure activities "quite a lot" or a "great deal"), and not due to another cause. Family adversity was defined by using 14 questions addressing housing, education, social relationships, and maternal health assessed prospectively at birth. We used multiple imputation to correct estimates of prevalence and association for loss to follow-up.

Results: Overall, 1995 teenagers had been tired for the last month, of whom 117 and 53 had chronic disabling fatigue of ≥ 3 and ≥ 6 months' duration, respectively. The estimated prevalence of chronic disabling fatigue of ≥ 3 and ≥ 6 months' duration was 2.07% and 0.94%, respectively, but increased to 2.44% and 1.30%, respectively, after imputing missing data. Prevalence was similar in boys and girls. The risk of chronic disabling fatigue increased with family adversity score (odds ratios: 1.25 [95% confidence interval: 1.09, 1.43] and 1.23 [1.01, 1.51] for ≥ 3 and ≥ 6 months' duration, respectively). Only 36 (30.77%) children with chronic disabling fatigue had consulted a doctor about their fatigue.

Conclusions: Chronic disabling fatigue is more common in families who experienced early family adversity and is often not reported to health care services.