An 8-year-old girl with a low platelet count was diagnosed with immune thrombocytopenia (ITP) but responded poorly to 17 days of first- and second-line treatment. During the period of treatment, the potential causes of ITP in children were searched, especially infections which are the most common cause of ITP in children. Finally, she was diagnosed with Hashimoto’s thyroiditis, and the platelet count recovered on the 3rd day of levothyroxine treatment and remained normal in follow-up. No case of Hashimoto’s thyroiditis associated with newly diagnosed paediatric ITP has ever been reported.