A prospective study of children with large congenital melanocytic naevi (CMNs) is in progress. Its aims are to observe the natural history and inheritance of CMNs, to record associated pathologies, and eventually to evaluate the effects of treatment. Information is obtained by patient-completed questionnaires and clinical assessment. One hundred and thirty-three children have been followed for a total of 452 patient years. The female/male ratio is 3:2. The characteristics, size and distribution at birth of the CMNs in this group of patients, and their development and associated abnormalities, are documented. After 5 years, affected children were compared with a matched cohort of normal children. Although the prevalence of neurological and developmental defects was higher in affected children, no malignant melanomas have been reported to date. The families of affected children had higher numbers of naevi and café-au-lait spots than those of normal children, suggesting a possible hereditary component. The mothers of affected children also reported an increased incidence of influenza-like illness and of severe nausea and vomiting in pregnancy. This study will continue for a further 4 years, in the first instance, after which we will seek relationships between characteristics of the naevi and outcome.

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