Developmental testing (7 children, aged between 17 months and 4 years) and intelligence profile analysis (38 children, aged between 4 and 16 years) were performed in a group of 45 children with NF1 followed at the Leuven NF clinic. Mental retardation (total IQ < 70) was noted in 2 of the 38 children between 4 and 16 years (5.2%). The mean total IQ of this group was 89.9 with a significantly higher verbal IQ than performed IQ. Factor analysis according to Kaufman showed a significantly weaker score on perceptual organization as compared with verbal comprehension. Concentration difficulty as measured by the Freedom from Distractibility Factor of Kaufman was not an important problem in the total group of children, but was more significant in the group of children with a total IQ above 85. Subtest analysis also showed significantly better scores on some verbal comprehensive tests as compared with some perceptual organization tests. Learning disabilities were frequent in the children analyzed in this report and non-verbal learning disabilities were the predominant type (40% of children). However other types and combinations of different types of learning disabilities were also found.