Positron emission tomographic (PET) images of visceral cancers are commonly visualized as "hot spots" of increased activity with relatively little normal anatomy discernable, when 2-[18F]-fluoro-2-deoxy-D-glucose (FDG) is used as the tracer. We describe a method by which computed tomography or magnetic resonance anatomic images can be digitally fused in three dimensions, using a rigid rotate-translate scale model with PET "metabolic" images, to simultaneously display registered anatomic and metabolic information. Such "anatometabolic" fusion images were produced in 10 patients with a variety of visceral cancers. External fiducial markers placed during both the anatomic and the metabolic study, as well as internal anatomic fiducials defined from landmarks observed on reconstructed transmission images, were used to achieve image fusion. The mean error magnitude +/- s.e.m. of fiducial registration in the nine patients with successful realignments was 5.0 +/- 0.8 mm. The mean accuracy in realignment between known anatomic structures seen on both the anatomic study and on the emission PET scan (but not used in realignment) was 6.3 +/- 0.8 mm. Localization of foci of increased FDG uptake to specific anatomic structures was achieved by this method, which represented an enhancement over the rudimentary anatomy available from the emission images alone. Anatometabolic fusion images made using this reasonably simple method should prove useful in the management of patients with cancer and other diseases.