The major clinical stigmata of basal cell naevus syndrome (BCNS) appear in adolescence and adult life but some occult skeletal abnormalities are congenital. BCNS is dominantly inherited and it would be useful to identify, as early in life as possible, which of the offspring of patients with BCNS are at risk of developing the syndrome. Radiographs of the neck and chest of 80 patients with BCNS diagnosed confidently on clinical criteria have been examined for abnormalities which were considered to be congenital skeletal anomalies. Congenital abnormalities of the cervical and thoracic spine, mainly spina bifida occulta, were found in 45%. Congenital abnormalities of ribs were found in 49% and of the shoulder(s) in 36%. Overall congenital abnormalities were shown on the neck or chest radiograph in 55 (69%) patients. The presence of one or more of these congenital abnormalities on the chest or neck radiograph of a child who is the offspring of a person with BCNS makes it extremely likely that the child also has BCNS. The absence of these features, and of any clinical features of BCNS, would suggest that the risk of the child developing BCNS has been reduced from the prior expectation of 50% to approximately half that (24%).