We studied a series of 27,145 consecutive infants with congenital defects and classified them into the currently recognized pathogenetic types of errors of morphogenesis, as defined by the International Working Group [Spranger et al., 1982: J Pediatrics 1:160-165]. Of all infants with congenital defects, 97.94% had malformations, 3.92% deformations, and 1.65% disruptions. Malformations associated with deformations were present in 3.12% of children with congenital anomalies, malformations with disruptions in 0.18%, deformations with disruptions in 0.07%, and malformations with deformations and disruptions in 0.14%. While deformations, including deformation sequences, were 2.38 times more common than disruptions and disruption sequences, isolated disruptions (1.27%) were more frequent than isolated deformations (0.59%). Knowledge of the frequencies of the different types of errors of morphogenesis (malformations, deformations, disruptions, developmental field defects, associations, complexes, unrecognized patterns of multiple congenital anomaly, and syndromes) may be of great value in the evaluation of patients with congenital anomalies.