We have developed a rapid screening method to detect a recurrent mutation in the neurofibromatosis type 1 gene. Using gene amplification and hybridization with allele-specific oligonucleotides, we screened 97 unrelated affected individuals for the recurrent C-->T substitution in codon 1947. The mutation was detected in 1 patient and found to cosegregate with the disease phenotype in the patient's family. Although the estimated prevalence of this mutation is low, rapid screening of different patient cohorts would identify multiple individuals carrying the same mutation. Such data would provide the first opportunity for examining correlations between phenotypic characteristics and molecular genotype and would allow clinicians to offer early diagnosis and prenatal screening to affected families. A format for the comparison of phenotypic features in other settings is presented.