Using a randomized controlled design, standard treatment of group cognitive-behavioral therapy (CBT) according to the Hesslinger protocol is compared to a newly developed group treatment specifically designed for adult patients with ADHD inattentive presentation (ADHD-I) called CBT for ADHD-I (CADDI). Research setting is psychiatric outpatient clinics. Research hypotheses include: 1. The CADDI protocol is more effective than standard treatment in terms of behavioral activation, procrastination, depressive symptoms, functional impairment, and quality of life, 2. Is equally effective in terms of ADHD symptoms, 3. Is more appreciated and tolerable, and 4. Outcome is mediated by mindful awareness. Effects are followed up at 6 and 12 months post treatment.

Inclusion Criteria:

1. Principal diagnosis of ADHD inattentive presentation
2. 18 years of age or older
3. If on medication, it needs to be well-established since three months, and
4. Prior psycho-educational intervention

Exclusion Criteria:

1. Intellectual impairment
2. Substance use disorder
3. Difficulties in adherence to medical or other treatment
4. Social and/or psychiatric problems to such an extent that they prevent focusing on treatment, or
5. Simultaneous psychological treatment