Mutations in the KAL-1 gene localized at Xp22.3 have been shown to be responsible for the X-linked Kallmann syndrome (KS), a disorder characterized by the association of hypogonadotropic hypogonadism and anosmia. In this paper, we describe the investigation of two families with X-linked KS, in which similar interstitial deletions ning exons 5 to 10 of the KAL-1 gene were identified. The presence of interspersed repetitive DNA sequences within the KAL-1 gene might have predisposed to this type of mutation.