Kallmann syndrome is characterized by hypogonadotropic hypogonadism and anosmia. Autosomal dominant, autosomal recessive, and X-linked patterns of transmission have been described. The X-linked form of Kallmann syndrome (XLKS) is the least common of the three modes of inheritance and is caused by mutations in the putative cell adhesion protein, KAL-1. In a large pedigree with XLKS, direct sequencing of the KAL-1 gene revealed a duplication of 11 base pairs in exon 1, resulting in a frameshift and a premature stop at codon 34 of the 680 amino acid protein. The clinical features of the affected individuals in this pedigree provide further evidence in support of the idea that XLKS is associated with neurologic features that are not seen in other forms of the syndrome.