PURPOSE: To heighten the awareness of the medical world to the importance of correct and rapid diagnosis in the presence of leukocoria in the child. METHODS: Starting with the presenting symptom, the authors present the guide lines to follow in a practical manner in order to reach a diagnosis in the principal retinal diseases causing leukocoria. RESULTS: A white pupil is due to retinoblastoma in almost half of all cases. Other possible causes, in order of frequency, are: persistent hyperplastic primary vitreous, Coats' disease, ocular toxocariasis, retinopathy of prematurity, retinal hamartomas. Diagnosis can usually readily be made by ophthalmoscopy, but may be problematic when the clinical presentation is atypical or in the presence of late complications. Age, sex, laterality, heredity, and in particular the presence or absence of calcifications and the size of the globe, are the main criteria for diagnosis. Ultrasonography plays a major role in this essential quest for correct diagnosis, quest which may ultimately lead to enucleation. CONCLUSION: Leukocoria in the child is a danger signal demanding certain diagnosis within the shortest possible time.