Parental ADHD may be a significant barrier to a successful treatment for the child's ADHD. The objective of our randomized controlled trial was to evaluate whether the treatment for maternal ADHD improves the efficacy of a behavioural parent training for children's ADHD. Patient enrolment and a description of the full analysis set (FAS) of mother-child pairs with non-missing baseline data are presented. One hundred and forty-four mother-child pairs were randomized to two treatments for maternal ADHD: cognitive behavioural group psychotherapy plus open methylphenidate treatment or control treatment (supportive counselling). After 3 months of treatment for maternal ADHD, mother-child pairs participated in a behavioural parent-child training. Assessment for eligibility included standardized instruments. After pre-screening out of 444 mother-child pairs, 206 were evaluated for trial participation and 144 were randomized. The FAS was built up by 143 dyads (children: mean age 9.4 years, 73 % males; mothers: mean age: 38.3 years). Fifty-two per cent of the children and 66 % of the mothers had combined ADHD subtype. Current axis-I co-morbidity rates were 48 % in children and 31 % in mothers. Maternal axis-II co-morbidity was 20.1 %. Fifty-seven per cent of the mothers lived together with the father of the index-child, and 29 % were single mothers. Sixty-two per cent had part-time or full-time employment. There was a selection bias excluding mothers with lack of time and effort for participation and mothers affected by coexisting mental and physical illness. Nevertheless, for our trial we were able to collect a sample comparable to routine psychiatric outpatient settings (registration: CCT-ISRCTN73911400, funding: BMBF-01GV0605).