Although single photon emission tomographic (SPET) imaging has been shown to be more sensitive than planar imaging in the diagnosis of pulmonary embolism, it has yet to be used routinely in clinical practice. The aims of this study were (1) to compare a new three-dimensional surface-shaded version of SPET (3-D SPET) with conventional planar imaging and coronal SPET slices, and (2) to evaluate observer agreement among these three modalities in the assessment of regional pulmonary perfusion. Compared with a consensus score (based on revised PIOPED criteria) of 29 cases, including nine with a clinical diagnosis of pulmonary embolism, 3-D SPET showed the highest number of normal scans, suggesting better specificity than planar or coronal SPET images. Five observers evaluated the three image sets twice within a 3-6 month period. Agreement with the consensus score was slightly better for the second reading and the average perfect agreement was 71-76%. No one image set was superior to any other in this respect. In conclusion, the number of normal scans using 3-D SPET is significantly greater relative to planar and coronal SPET scans as defined by the consensus view. Observer agreement rates are very similar with all three modalities.