The sacral region and perineum, already introduced in Chapter 83, are presented in greater detail in this section. First, the simple operation of pilonidal cystectomy (Chapter 98) is described as a means of illustrating the anatomy of the sacrum and the presacral region. This is often one of the first operations performed by the beginning surgeon, yet results are often less than perfect, and numerous modifications of the operation exist. Two of these, marsupialization and z-plasty, have emerged as dominant and are described in this chapter.