Due to the development and refinement of computed tomography (CT), sonography, and interventional techniques, the field of interventional radiology has seen tremendous growth in recent years. In particular, the precise anatomic detail provided by CT and sonography has allowed percutaneous biopsies and abscess drainages to be performed safely and effectively. Percutaneous biopsies are now becoming the most common interventional radiographic procedures in many institutions. The usual indications for a biopsy are to determine the etiology of a mass, neoplasm, or inflammation, and to determine whether masses in known oncologic patients represent scarring or residual viable tumor. Accuracy rates for most percutaneous CT-directed biopsies are well over 90%, and the complication rate is very low. CT-directed percutaneous abscess drainages are also safe and effective and, in most cases, will be preferable to surgical drainage. The initial indications for percutaneous drainage (single, unilocular fluid collections) have been greatly expanded to include multiloculated collections, interloop abscesses, periappendiceal abscesses, and even percutaneous cholecystotomies. Biopsy and drainage procedures, together with their accuracy rates, indications and complications, are reviewed in this monograph.