We describe a patient with incontinentia pigmenti who developed the clinical picture of intestinal Behçet's disease. Diagnosis of Behçet's disease was base on a recurrent genital and oral ulcer and a positive HLA-B51. Impaired neutrophil chemotactic activity and an elevated plasma IL-6 level were found. Chromosomal study revealed no abnormality in the patient or her family. We discuss the possibility that there are common immunological abnormalities in the two syndromes.