X-linked recessive ichthyosis (XLI) is a genodermatosis characterized by dark, adhesive, polygonal and regular scales of the skin on scalp, posterior ears, neck, trunk and limbs; palms and soles are spared. XLI is caused by a mutation of steroid sulfatase (STS). Deficiency of STS increases levels of cholesterol sulfate in the stratum corneum, which appears to be responsible for the scaly skin in XLI patients. More than 90% of XLI patients harbor deletions of the entire STS gene and flanking sequences whereas seven partial deletions and 14 point mutations of the STS gene have been reported worldwide. A 39-year-old female with no skin lesion visited our department with her brother to take gene analysis before pregnancy. The woman had no skin lesion, but her brother had dark, polygonal and regular scales on the whole body, consistent with the clinical feature of X-linked ichthyosis. Males of her mother’s family also have same skin lesion as the patient. Diagnostic exome sequencing identified an entire deletion of the STS gene in her brother, but the woman was proved as an unaffected female by chromosomal microarray.