The authors evaluated clinical and epidemiologic features of neurofibromatosis type 1 (NF-1) as predictive factors of severity of the disease. The data were retrieved from medical records of 110 children with NF-1 followed up during the period 1974-1991 (mean duration of follow-up 6.7 years). Presence of macrocephaly correlated with higher grade of severity of the disease (P = 0.018). Familial NF-1 was more common in patients with grade 4 disease than in children with grade 1 severity (P < 0.05; odds ratio 2.9, confidence limits 0.85-10.5). The specificity of positive family history and macrocephaly as predictive factors for the grade 4 disease was 90% and 89%, respectively, and sensitivity was 71% and 36%, correspondingly. Positive predictive value of familial NF-1 and macrocephaly was 24% and 31%, respectively. In conclusion, although patients with family history of NF-1 and with macrocephaly tend to have more severe disease, the clinical utility of these features as predictive factors for severity is limited.