PURPOSE: Subperiosteal orbital lesions are most commonly abscesses secondary to sinusitis but, in rare cases, may represent other processes. Here, the authors compare the clinical and radiographic presentation of subperiosteal abscesses and alternate subperiosteal processes ("masqueraders") in an effort to establish distinguishing preoperative diagnostic criteria. METHODS: A retrospective chart review of cases of subperiosteal orbital lesions that underwent surgical intervention over a 3-year period was performed. The medical records of 6 cases of subperiosteal masqueraders and 6 cases of abscesses were reviewed for the clinical course, imaging (including radiographic density of lesions), and pathology. Clinical and radiographic features of the 2 groups were compared. RESULTS: All cases presented with orbital signs on exam. Fever and leukocytosis were absent in the masquerader group and present in 3 patients from the abscess group. Common radiographic findings in both groups included a rim-enhancing convex mass along the orbital wall and adjacent sinus opacification, often with bony dehiscence. Of the masqueraders, the final diagnosis was hematoma in 3 cases, mucocele in 1, and malignancy in 2. The difference between the mean radiodensity of the subperiosteal abscesses, 38 ± 5 Hounsfield units (95% CI, 34-42), as compared with the average radiodensity of the masqueraders, 71 ± 5 Hounsfield units (95% CI, 67-75), was significant (p = 0.042). Comparing radiodensity of the orbital lesion to adjacent sinus lesions and metastatic lesions elsewhere was also informative in establishing the diagnosis. CONCLUSIONS: Radiographic features, particularly radiodensity, may help distinguish subperiosteal abscesses from other lesions and aid in preoperative diagnosis and management.