Despite impaired mother-child interactions noted in youth with attention-deficit/hyperactivity disorder (ADHD), there is no such information for their siblings. This study aimed to test whether the affected and unaffected siblings, like youth with ADHD, also encountered impaired mothering and mother-child relationships as compared to typically developing youth (TD). The sample consisted of 122 probands (107 males, 87.7 %), aged 10-16, with DSM-IV ADHD, 44 affected (26 males, 59.1 %) and 78 unaffected (28 males, 35.9 %) siblings, and 122 TD youth. Both participants and their mothers received psychiatric interviews (K-SADS-E) about the participants and reported maternal parenting style, mother-child interactions and child behavioral problems at home. Based on both reports, probands with ADHD and affected siblings (only youth report) had more impaired relationships, more behavioral problems at home, and less perceived family support than unaffected siblings and TD youth. Probands with ADHD had higher maternal authoritarian control than unaffected siblings. The findings suggest that impaired mothering, mother-child interactions, and family support are related to the presence of ADHD diagnosis in both probands and their affected siblings.