Sacrococcygeal teratomas are neoplasms that may include all three germ layers (totipotential cells), can contain both solid and cystic components, and are more common in the pediatric age group and females. These tumors can contain tissues from almost any organ system including digestive, nervous, respiratory, and skeletal [37]. Histologically, tumors are referred to as either mature or immature, which reects the degree of cellular differentiation. The more recognizable the elements (hair, bone, teeth) the more likely the tumor is to be benign, although all should be viewed as potentially malignant. Cystic components are typically benign whereas solid components are more often associated with malignant degeneration. The tumors can reach considerable size and diagnosis is often delayed (Fig. 21.6a–c). Teratomas are often associated with anomalies of the vertebra, urinary tract, and anorectum [38]. The rate of malignancy correlates strongly with age, being much less common beyond the sec­ond decade [20, 39]. In infants only 7% of girls and 10% of boys presented with malignancy prior to 2 months, whereas the rates can be as high as 48% and 67%, respectively, after 2 months of age [40]. Malignant degeneration can occur in adults, and incomplete or intralesional resection increases the likelihood of malignant degeneration [41–43]. Because of the diverse germ cell layers these lesions can transform into squamous cell carcinoma (ectodermal origin), rhabdo­myosarcoma (mesenchymal origin), or anaplastic (indeter­minate cell of origin) tumors [3].