A wide variety of focal and diffuse infectious processes involve the abdomen. At one extreme are diseases such as pyelonephritis, cystitis, and pelvic inflammatory disease, conditions usually diagnosed without imaging studies and treated without complications. At the other extreme are abdominal abscesses, which may defy clinical diagnosis, are associated with significant morbidity and mortality, and may remain undetected or insufficiently characterized in spite of multiple imaging studies. The limited diagnostic value of clinical evaluation and plain film radiography in abscess detection has lead to widespread use of sophisticated imaging techniques including Gallium-67 (67Ga) scintigraphy, Indium-111 WBC (111In-WBC) scintigraphy, computed tomography (CT), and ultrasonography (US). Abdominal abscesses occur in a wide variety of anatomic sites, may involve any abdominal organ system, and have a number of different causes. The heterogeneity of the disease process and the varying capabilities of the different imaging techniques (with respect to site and organ system) make reliance on a single technique undesirable. An algorithmic approach using 67Ga or 111In-WBC scintigraphy, CT, and US provides a logical and clinically practical approach to complicated abdominal infection. By recognizing differences in clinical presentation and by appreciating the diagnostic strengths and weaknesses of nuclear medicine, CT, and US, the algorithm provides a reliable and direct route to accurate diagnosis while minimizing unnecessary examinations.