Objectives. Inquiry the behaviour and emotional problems in siblings of children with ADHD and Autistic Spectrum Disorders (ASD); analyse the psychological symptoms of the mothers of children with ADHD and ASD; the assessment of a possible relationship between the psychological problems of the mothers and the emotional and behaviour problems of siblings. Method. We studied 67 siblings and their mothers, 23 siblings of children with ADHD (with 23 mothers) 21 siblings of children with ASD (with 21 mothers) and 23 siblings of normal children (with 23 mothers) in which we applied the following instruments: Child Behaviour Checklist (CBCL) for the siblings and Symptom checklist (SCL-90-R) for the mothers, both instruments were completed by mothers. Results. The emotional and behaviour problems and the psychological symptoms of the mothers of siblings of children with ADHD and ASD are emphasized than the mothers and the siblings normally developed. The psychological stress of mothers of children with ASD and of children normally developed is related with the emotional and behavioural problems of siblings. factors and the problems in family functioning we’ll help us to have an therapeutically approach of the family.