OBJECTIVE: To establish the frequency of minor disease features in children with neurofibromatosis type 1 (NF1) and to evaluate the value of minor disease features in children < or = 6 years with a suspected diagnosis of NF1, considering that the disease is virtually 100% penetrant at 6 years of age. DESIGN: During this 10 year, prospective, multidisciplinary, follow up study, 209 children suspected of having NF1 were examined; 150 were diagnosed with NF1 and 59 were not. The present analysis included children in whom NF1 was considered to be present at 6 years of age (n=85) and children without NF1 at 6 years of age (n=42). RESULTS: The minor disease features macrocephaly (52.9%), short stature (24.7%), hypertelorism (63.5%), and thorax abnormalities (37.6%) were highly prevalent in children with NF1 and significantly associated with a diagnosis of NF1 at 6 years of age. In addition, the mean number of minor disease features was significantly higher in children with NF1 at 6 years of age compared to the group without a diagnosis at 6 years of age (mean 1.8 v 0.8, p<0.001). Moreover, children with three or more minor disease features were all diagnosed with NF1 under the age of 6 years. Multivariate analysis using a logistic regression model showed that macrocephaly, short stature, hypertelorism, and thorax abnormalities were all independently associated with the presence of NF1 at 6 years of age. CONCLUSION: In children with insufficient diagnostic criteria aged < or = 6 years, documentation of minor disease features may be a helpful aid in predicting the diagnosis of NF1 in years to come.