Today, many patients with lymphoma are cured by polychemotherapy and irradiation. However, residual masses are frequently observed after treatment and discrimination between vital tumor and inactive fibrotic tissue by computed tomography or magnetic resonance tomography is often not possible. 18F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a metabolic imaging modality that is able to detect active lymphoma lesions. The application of PET may play a crucial role in identifying patients with residual disease and contribute valuable prognostic information. To assess the prognostic implications of PET in the post-therapeutic setting, we performed a MedLine Search and reviewed the current available studies on this important issue together with our own data.