Abstract Introduction The objective of this study was to assess the evolution of stress in families of children and adolescents who start psychopharmacological treatment after being diagnosed with attention deficit hyperactivity disorder (ADHD), and the ability to detect this change using the FSI (Family Strain Index) questionnaire. Methodology Forty-eight (48) specialists in child–adolescent psychiatry or neuropediatrics included 429 families of children diagnosed with ADHD, represented by the father, mother or guardian of the child. In the baseline visit, and at two and four months, the intensity of the symptoms of ADHD was evaluated using the Abbreviated Conners Scale, and family stress was evaluated using the FSI questionnaire. Results The following was observed: (a) an improvement in the overall FSI score and in all its dimensions (P Conclusions There was a significant relationship between the positive evolution of symptoms in children with ADHD and the reduction of family stress, as evaluated by the FSI questionnaire, after starting psychopharmacological treatment. This study showed a great sensitivity to change in the clinical situation of patients with ADHD, evaluated through the stress it produces on its families. It is recommended to use this questionnaire as an indirect measurement of the repercussions of the disorder on the environment of the child with ADHD in terms of family stress.