It is well recognised that thyroid disorders may present with a wide range of symptoms and signs in adults and children. We describe an unusual presentation of thyroid disease in an adolescent with psychiatric symptoms, in whom normalisation of his thyroid function resulted in significant improvement in his mental state. Although agitation and depression are commonly listed as symptoms of hyper- and hypothyroidism, respectively, presentation to psychiatric services is not well documented in the adolescent age group and thyroid function tests are not a routine inclusion as part of a paediatric psychiatric assessment.