Immune thrombocytopenia (ITP), an acquired autoimmune disorder of low platelets and risk of bleeding, has a substantial impact on health-related quality of life (HRQoL). Patients with ITP often report significant fatigue, although the pathophysiology of this is poorly understood. In this observational cohort of 120 children receiving second-line therapies for ITP, we assessed reports of fatigue using the Hockenberry Fatigue Scale. Children and adolescents with ITP reported a similarly high level of fatigue with 54% (29/54) of children and 62% (26/42) of adolescents reporting moderate-to-severe fatigue. There was no correlation between fatigue and age or gender. Adolescents with newly diagnosed and persistent ITP had higher mean fatigue scores than those with chronic ITP (P = 0·03). Fatigue significantly improved in children and adolescents by 1 month after starting second-line treatments, and this improvement continued to be present at 12 months after starting treatment. Fatigue scores at all time-points correlated with general HRQoL using the Kids ITP Tool, but did not correlate with bleeding symptoms, platelet count, or platelet response to treatment. Fatigue is common in children and adolescents with ITP and may benefit from ITP-directed treatment even in the absence of bleeding symptoms.