OBJECTIVE: To establish the prevalence and incidence of symptoms and complications in children with neurofibromatosis type 1 (NF1) and to assess possible risk factors for the development of complications. DESIGN: A 10 year prospective multidisciplinary follow up study. PATIENTS: One hundred and fifty children diagnosed with NF1 according to criteria set by the National Institutes of Health. RESULTS: In 62 of 150 children (41.3%) complications were present, including 42 (28.0%) children with one complication, 18 (12.0%) with two complications, and two (1.3%) with three complications (mean (SD) duration of follow up 4.9 (3.8) years). Ninety five of the 150 children presented without complications (follow up, 340.8 person-years). The incidence of complications was 2.4/100 person-years in