This practical volume is intended for all radiologists, gastroenterologists, and surgeons who are responsible for, or interested in, the diagnosis and care of patients with diseases of the anal and perianal region. After an introductory section focusing on surgical, MRI, and US anatomy, up-to-date clinical and therapeutic information is provided on the full range of perianal inflammatory conditions, with special attention to Crohn disease, ulcerative colitis, and sexually transmitted diseases. Physical and surgical examination is carefully discussed, with consideration of limitations, results, clinical needs, and the questions likely to be posed of imaging. The subsequent three sections provide detailed information on the different imaging modalities: transanal and transperineal ultrasound, contrast-enhanced MRI, and CT. Techniques, diagnostic accuracy, common and unusual disease patterns, artifacts, and pitfalls are clearly presented.