In the last decades there was an increasing interest in early detection of prodromal symptoms in schizophrenia and, more specifically, in detecting subjects at high risk for psychosis. However, especially in case of childhood-onset schizophrenia (COS), sometimes it is possible to don't recognize its early symptoms and to ascribe the observed clinical picture to other diseases, with consequent delay in diagnosis and treatment of these patients. In this case report we want to underline the importance of an early detection of schizophrenia, with a focus on differential diagnosis between Attention Deficit/Hyperactivity Disorder and schizophrenia.