Forty-one children, ranging in age from 1 month to 14 years, had six or more cafe au lait spots at their initial visit and were examined annually. Signs of neurofibromatosis type 1 eventually developed in 24. The most common feature to appear to confirm the diagnosis was skin-fold freckling, which occurred in 18 subjects. Diagnosis was based on the appearance of Lisch nodules in 5, and on neurofibromas in 3. In most instances, diagnosis was established within 3 years of initial evaluation, usually before 5 years of age. Six children had a segmental distribution of cafe au lait spots, suggesting segmental neurofibromatosis. In 3, diagnoses other than neurofibromatosis type 1 were established (Bannayan-Riley-Rulvalcaba syndrome, multiple lentigines syndrome, and fibrous dysplasia). In 8 subjects only multiple cafe au lait spots are present, and no definite diagnosis has been established. It is concluded that with regular follow-up, including physical and ophthalmological examinations, a definite diagnosis, most commonly neurofibromatosis type 1, can be established for most children having multiple cafe au lait spots.