Pituitary hyperplasia secondary to primary hypothyroidism (PHPH) is uncommon in children and is reversible with thyroxine therapy. We report an Omani girl who presented at the age of 13 years and 6 months with profound primary hypothyroidism due to Hashimoto's thyroiditis and secondary pituitary hyperplasia and hyperprolactinemia. Pituitary magnetic resonance imaging confirmed the presence of pituitary hyperplasia which regressed during follow-up after the administration of thyroxine therapy. The diagnosis of PHPH is very important in both children and adults in order to avoid unnecessary brain surgery or medical treatment for a presumed pituitary mass or adenoma. To our knowledge, this patient represents the first case of an Omani child presenting with PHPH.