['Our clinical observations raised concern that teenagers and young people with neurofibromatosis type 1 (NF1) might feel lonely and we decided to investigate their experiences and compare them with unaffected siblings. We also assessed predictive factors of loneliness.', 'We evaluated 60 NF1 patients aged 17 (±3.1) years and 23 siblings aged 17 (±2.9) years with a self-report questionnaire that assessed loneliness, depression, shyness, self-esteem, social support, bullying and difficulties making friends. Objective assessments of NF1 disease severity and visibility and somatic NF1-related and social support-related variables were carried out. Multiple linear regression analysis was performed.', 'Of the 60 patients with NF1, 11 (18%; CI: 8-28%) said that they felt lonely often or always and felt a higher degree of loneliness, but none of the siblings said that they felt lonely. Predictors of loneliness were depression, shyness, bullying, self-perceived conception of illness burden and a low level of social support from friends.'] Are teenagers and young adults with neurofibromatosis type 1 more likely to experience loneliness than siblings without the illness?