Children with neurofibromatosis type 1 (NF1) have difficulties in forming friendships and are often rejected by their peers. Factors that contribute to these negative social outcomes are poorly understood. This study investigated the social skills of children with NF1 and the influence of comorbid conditions, such as attention-deficit-hyperactivity disorder (ADHD) and specific learning dfficulties. We assessed and analyzed data from 79 children with NF1 (42 males, 37 females; mean age 11 years 6 months, SD 2 years 4 months) and 46 unaffected siblings (19 males, 27 females; mean age 12 years 1 month, SD 2 years 6 months; age range 8 to 16 years). Social skills were measured with the Social Skills Rating System. Children with NF1 had significantly poorer social outcomes than their unaffected siblings, and significantly poorer social skills in comparison with normative data. The presence of ADHD (in 39% of children with NF1) was the major risk factor for poor social functioning. Children with NF1 and ADHD had the poorest social skills and social outcomes when compared with children with NF1 only or children with NF1 and learning difficulties. These findings dispel the previous assumption that NF1 alone is associated with poor social functioning and has major implications for the development of effective interventions.