This 16-year-old girl with a history of mental retardation and a generalized seizure disorder was found to have hypopigmented patches distributed along the Lines of Blaschko. Areas of hypopigmentation were most prominent on her left lateral thigh. Various reports have found that 33-94% of patients exhibiting aberrant pigmentation along the Lines of Blaschko have neurologic, skeletal, and/or ocular abnormalities. However, more recent case series suggest that there is a bias in many reports, and the incidence of associated findings is probably much lower than previously thought. Dyschromia along the lines of Blaschko is now recognized as a sign of genetic mosaicism which may be associated with extracutaneousl findings.