This study evaluates and compares the accuracy of positron emission tomography with 18F-fluoro-2-deoxyglucose (FDG-PET) and gallium-67 citrate (Ga-67) scintigraphy in identifying disease sites in patients with malignant lymphoma at initial diagnosis or relapse. Histology subgroups included low (n=5), intermediate (n=6), high-grade (n=5) non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD) (n=14). Ann-Arbor staging included 7 patients in stage I, 8 in stage II, 9 in stage II, 6 in stage IV and 11 extra-nodal. In this study, before any therapy, 25 contemporaneous FDG-PET and Ga-67 scintigraphies were performed on patients with either NHL (16) or HD (14). One hundred and eleven sites of disease were correlated on a site-by-site basis in corresponding areas of FDG-PET and Ga-67 scintigraphy. Discordant FDG-PET and Ga-67 scintigraphic findings were correlated with CT/MRI and clinical evaluation. FDG-PET detected malignant lymphoma in 24/25 patients (sensitivity: 96.0%). There was a false-negative FDG-PET result in only 1 patient with low-grade gastric malignant lymphoma. Ga-67 scintigraphy detected malignant lymphoma in 18/25 patients (sensitivity: 72.0%). There were false-negative Ga-67 scintigraphic results in 4 cases with low-grade non-Hodgkin's lymphoma, 2 cases with bone or bone marrow involvement, and 3 smaller disease sites. FDG-PET upstaged 6 patients in whom Ga-67 scintigraphy detected disease sites partially. In imaging lymphoma prior to therapy, FDG-PET had a higher sensitivity and detected significantly more disease sites when compared with Ga-67 scintigraphy in the initial evaluation of this group of patients. Upstaging of patients with FDG-PET may result in a change in treatment strategy. However, evaluation of the final sensitivity, specificity and accuracy of these imaging modalities will need a further study with a larger patient number.