Prospective examination of the ocular fundi was carried out in the newborn female sibling of a girl with incontinentia pigmenti and bilateral retinopathy. At age 3 months the new baby's peripheral retina was found to be avascular in both eyes. At age 2 years progressive vascular proliferation at the watershed area between normal and abnormal retina led to bilateral vitreous haemorrhage. The new vessel tufts promptly regressed when the avascular area in each eye was treated by single-freeze cryotherapy and the blood in the vitreous absorbed. Cicatricial retinopathy was thereby prevented. Prospective retinal examination of newborn female siblings of children with incontinentia pigmenti is advised, with early cryotherapy recommended if progressive neovascularisation is detected.