Inclusion Criteria:  Age 6 to 18 years Documented clinical diagnosis of autism spectrum disorder according to DSM IV or DSM V and comorbid behavioural problems To start treatment with risperidone  Exclusion Criteria:  Diabetes type I or II Congenital or acquired syndrome associated with changes in appetite, body weight or lipid profile (e.g. Prader Willi) Treatment with antipsychotic medication within the last 6 months Known Long QT syndrome (LQTS) Pregnancy