An important area of occupational therapy is to assist people in finding activity balance in their daily lives. People with the neuropsychiatric disorders ADHD and Asperger syndrome often have difficulties that may be linked to this. The aim of this study was to describe how occupational therapists reason and work with activity balance with people who have ADHD or Asperger's syndrome. Eight semi-structured interviews were conducted with occupational therapists who work with these diagnostic groups. The data were analyzed using qualitative content analysis and resulted in three categories: Balance and imbalance affects the activity areas; person and environment impact on activity balance; Enabling activity balance. The results showed that occupational therapists often work with activity balance with these diagnostic groups by creating balance between activity areas and awareness of what gives and takes the energy of the person. The reasoning by the occupational therapists' revealed that the person's motivation, knowledge and personal qualities was relevant to the activity balance and that the environment affects the person's everyday functioning. The occupational therapists enables activity balance through their assessments, various interventions, and in how they use themselves throughout the occupational therapy process. This study contributes to the knowledge of how occupational therapists reason and work with people with ADHD and Asperger's Syndrome and their activity balance.