With the advent of combined modality imaging, it has become essential for the radiologists how structure and function relate to each other. Previously radiologists had to rely upon CT or MRI in order to tell the location of a problem but could not assess functionally what was going on within the patient. PET image has allowed radiologists to make a functional assessment to aid in the diagnosis and treatment planning for patients. This issue reviews the use of PET/CT and PET/MRI to evaluate patients with neurologic disorders, malignant and nonmalignant thoracic disorders, the cardiovascular system, breast diseases, musculoskeletal system, abdominal and pelvic disorders, and endocrine disorders.