Table 1 Inclusion and exclusion criteria

- Age between 8 and 18 years

- Able to speak, write, and read Dutch

- Diagnosed with mitochondrial disease (genetically confirmed)

- Being severely fatigued (CIS fatigue severity ≥35)

- Access to a computer with internet connection

- Basic computer skills

- Able to travel to the hospital for the CBT intervention (3 sessions)

- Intellectual disability (developmental age younger than 8 years).

- Primary depression (CDI ≥16) or anxiety disorder (SCARED-C ≥ 25)

- Current psychological treatment for fatigue