Cranium bifidum is literally "cleft skull." Numerous reports describe the anatomy of this defect, and crude estimates of the population prevalence suggest it is a relatively infrequent occurrence. McKusick's catalog contains only one family with cranium bifidum but several familial reports of symmetrical parietal foramina. Available information indicates that cranium bifidum and symmetrical parietal foramina are inherited in an autosomal dominant fashion and occur in orientals, blacks, whites, and native Americans. Here we report on a family with serial radiographs that document ontogenic development of parietal foramina in late childhood and adulthood from apparent cranium bifidum and parietal foramina during infancy and early childhood. We conclude that these are the same entity, differentiated only by the time during life in which the defect is demonstrated.