The Attention Deficit Disorder and Hyperactivity (ADDH) is now, a frequent diagnosis in Paediatrics Psychiatry. This real neurobiological syndrome has a variable incidence (3-12%), an early beginning (before 7 years) and an important permanency in adult age (15-20% keep diagnosis and 65% residual symptoms). It represents a risk factor for posterior psychiatric diseases, antisocial behaviour and relation problems. This makes the early diagnosis and treatment necessary. The 70-90% of the patients responds to simpatico mimetic treatment and the methylphenidate is the most used. Patients must carry out the clinical criteria and nowadays there is not any recognized helpful test for the diagnoses except the clinical one. The medium latency auditory evoked response (MLAER) appears 10-70 ms after the cochlear receptor activation and it has cortical and subcortical generators.

We studied MLAER in ADDH: their morphology, changes with treatment and relation between morphology changes and clinical response to treatment.

Patients (53) had ADDH clinical criteria, methylphenidate treatment chosed, not comorbidity neither hearing loss. First phase without treatment and second with it where we did MLAER and tronco-encephalic auditory evoked response during wakefulness and sleep.

Without treatment 76% responses were asymmetric (51% of them with a specific type). The rest 23% were normal. With treatment 63% changed the morphology and 70% had a good response to treatment. Only 11% of patients without alterations had a good clinical development.

An ADDH diagnosis has different physiopathologic mechanism. The MLAER in ADDH could predict the treatment response.