Late cutaneous signs of incontinentia pigmenti (IP) are often subtle and misdiagnosed. We focus on these somewhat confusing clinical markers in a family, and on the genotypic diagnosis based on DNA analysis. An infant was born with a typical IP rash. Dermatologic examination of the women in her family revealed that her mother, her maternal aunt, and her grandmother had subtle skin signs reminiscent of IP. The four family members proved to be informative for DNA markers in the Xq28 region. Familial cases of IP are sometimes missed due to the lack of recognition of some late skin signs that are not always hyperpigmented streaks. Subtle, faint, hypochromic or atrophic lesions in a linear pattern may occur. Thus an accurate diagnosis of the women in a particular family also requires anamnestic data and recognition of extracutaneous anomalies. When a clinical diagnosis has been made, DNA marker analysis allows us to offer a prenatal diagnosis with minimal risk of error in case of further pregnancy. However, early testing of chorionic villus samples does not allow one to predict the severity of the disease in an affected fetus.