A relationship exists between tumours and malformations both generally and in particular combinations. This is also valid for minor errors of morphogenesis suggesting that embryonic tumours are an expression of aberrant intra-uterine morphogenesis. We speculated that these minor aberrations might also manifest in other morphological defects, especially in minor anomalies and malformations of the ribs. We reviewed chest roentgenographs of 1000 children with malignancies for rib anomalies and compared them to 200 patients with mainly infectious diseases. We found 242 rib anomalies in 218 children with tumours (21.8%) and 11 (5.5%) in children without malignancy. This difference was statistically highly significant (P less than 0.001). A high incidence of cervical ribs was found in neuroblastoma (33%), brain tumour (27.4%), leukaemia (26.8%), soft tissue sarcoma (24.5%), Wilms tumour (23.5%) and Ewing sarcoma (17.1%). Only neuroblastoma showed a high incidence of rib bifurcation (4.5%). The increased incidence of these mesenchymal defects in children with malignancies may be another clue for an altered morphogenesis in tumour origin. In neuroblastoma the rib anomaly may be another expression of neurocristopathy as proposed for the association of congenital heart disease and neuroblastoma.