Objective: To present the clinical, genetic, biochemical, and molecular findings in two Chinese siblings with X-linked recessive Kallmann syndrome (KS). Design: Case report. Setting: University medical center. Patient(s): Two Chinese siblings. Intervention(s): Clinical evaluation, hormone assays, and gene mutation research. Main Outcome Measure(s): Endocrinologic evaluation and genetic analysis. Result(s): A missense mutation of KAL1, c.1828G>A, led to pVal610Ile substitution in two brothers with KS; their mother is heterozygous for this missense mutation encoded by single-nucleotide polymorphism rs2229013. Conclusion(s): Mutation analysis revealed that a missense mutation of KAL1 in two brothers with KS, while their mother was heterozygous for this missense mutation encoded by the single-nucleotide polymorphism rs2229013. Variant alleles of KAL1 related to X-linked recessive KS expand the spectrum of KAL1 mutations causing KS. ((c) 2013 by American Society for Reproductive Medicine.)