A series of 342 patients with unilateral exophthalmos underwent orbital diagnostic studies including ultrasonography, computerized tomography, radiographic studies, and vascular contrast studies. Each test was found to have diagnostic capabilities that complemented other studies depending upon the specific disease process involved. No one test was entirely adequate without supplementary information from the other tests. Radiographic studies demonstrated bony abnormality in 50% of the tumor cases, but in only 28% of the entire series of exophthalmos cases. Computerized tomography demonstrated diagnostic soft tissue abnormality in 86% of tumors, 43% of inflammatory diseases, and an overall yield of 62% positive results. Ultrasonography proved the most versatile test for evaluation of orbital soft tissues, with 80% positive results for tumors, 87% for inflammatory disorders, and 78% overall accurate orbital diagnosis. Erroneous tumor diagnosis of 7% with computerized tomography and 3% with ultrasonography were corrected by combining these two studies, because they tend to err in opposite directions. Combination of ultrasound and CT scan resulted in a 98% correct diagnosis of all types of orbital diseases.