Kallmann's syndrome (KS) refers to the association of hypogonadic hypogonadism and anosmia or hyposmia. The X-linked form of the disease is due to mutations in the KAL1 gene that encodes for the protein anosmin-1. We studied the KAL1 gene in a patient with KS and his family by PCR amplification and direct sequencing. A novel missense mutation (V263G) that modifies the major cell adhesion site of the anosmin-1 protein was identified. Our results suggest that this reported mutation is responsible for KS and might help to elucidate the function of an important area of the anosmin-1 protein.