Neurofibromatosis type 1 (NF1) is increased about 150‐fold in autistic patients. The aim of this study was to test for an association between the NF1 locus and autistic disorder. The allele distributions of three markers of the NF1 gene were studied in 85 autistic patients and 90 controls. No differences in allele distributions were observed. However, we found a new allele (allele 5) of the GXAlu marker in four autistic patients. Allele 5 was absent in a larger control population (213 individuals). The patients with allele 5 had a more severe clinical picture, mainly in the fields of motility and tonus. Our preliminary results suggest that the NF1 region is not a major susceptibility locus for autism. However, the GXAlu marker of the NF1 gene appears as a possible candidate for a susceptibility locus in a small subgroup of severely affected autistic patients. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:729–732, 1999. © 1999 Wiley‐Liss, Inc.