The objective of this study was to explore the behaviour, including sleep patterns, of children with neurofibromatosis type 1 (NF1). For this purpose we designed a cross-sectional descriptive survey conducted by postal enquiry with telephone follow-up. Simonds and Parraga's sleep questionnaire and the Strength and Difficulties Questionnaire were used to screen sleep patterns and behaviours respectively. Information was obtained for 64 children (39 male, mean age 10 y 7 mo, SD 4 y 1 mo, range 3 to 18 y; 57% response rate). There were increased numbers of children with NF1 achieving scores in the borderline and abnormal range for ratings of peer problems (p < 0.001), hyperactivity (p < 0.001), emotional symptoms (p < 0.001), and conduct disorder (p < 0.05). Total difficulties score was also high (p < 0.001) in the NF1 group. Only one group of sleep problems, parasomnias (in particular sleepwalking and sleep terrors), had a higher occurrence (p < or = 0.05) in the NF1 group than in the general population. Within the NF1 group, conduct problems (p < or = 0.05), hyperactivity (p < or = 0.01), emotional problems (p < or = 0.01), and the total difficulties score (p < or = 0.01) were all significantly higher in children with frequent sleep disturbance. We conclude that NF1 is associated with sleep and behavioural problems in a high proportion of children. Psychiatric conditions, e.g. attention-deficit-hyperactivity disorder, may be underdiagnosed on a large scale in children with NF1, and the use of simple screening tools in clinical settings may prove beneficial.