Ultrasound scanning plays an important role in evaluating the extent of benign and malignant anorectal and pelvic diseases. This chapter discusses this important method for evaluating rare anorectal and pelvic neoplasias, one that allows for the quantification of the exact circumferential and longitudinal extension of the lesion into the rectal wall or adjacent tissue and the relationship between the lesion and the sphincter muscles. This is the most important aspect to consider when planning surgical resection with or without sphincter-saving. In addition, the three-dimensional scanning mode is safer, making it possible to review the images posteriorly, in real time, as required by some lesions.