Papillary thyroid carcinoma (PTC) is the most common form of thyroid tumour in childhood. Different studies reported higher risk of developing a PTC in Hashimoto’s thyroiditis patients (HT) even in paediatric-adolescent age, although real incidence and risk factors are unknown. The paper describes the case of a girl, diagnosed with HT and hypothyroidism at the age of 11, who developed thyroid ultrasound alterations after two years. The histological examination of the satellite lymph node confirmed the diagnosis of PTC. A total thyroidectomy was performed. The follow up scintigraphy did not show disease residues, so no indication was given to radioiodine therapy. The case report underlines the importance of an accurate thyroid and lymph nodes ultrasound monitoring in children with autoimmune thyroiditis, in order to highlight possible malignancy development.