Abstract Background Thought and language disorders are main features of adults with schizophrenia and bipolar disorders however studies on such abnormalities are scant in young patients with very early onset psychosis (VEOS). The aim of the present study is to assess the relationship between language and thought disorders in patients with very early onset schizophrenia (SCZ), schizoaffective disorders (SCA) and bipolar disorders (BD). Method Forty-one patients (18 SCZ, 16 BD, and 7 SCA) with mean age less than 15 years old were assessed through a series of neurocognitive and psycholinguistic tests, including the Thought, Language and Communication Scale (TLC). Results SCZ group performed worse in all tests as well as the TLC, followed by SCA and BD groups respectively. Thought disorders were related to deficits in executive functioning and semantic processing, and the metaphors’ test was the best predictor of TLC functioning. Discussion TD in SCZ, SCA and BD are one of the most important features in patients with VEOS and that the evaluation of metaphor comprehension can be an important instrument in the early detection of this disorder.