The clinicopathologic features and the results of diagnostic studies were reviewed in five patients with primary orbital liposarcoma. The major clinical complaints were diplopia and proptosis; visual function was typically well maintained. In three cases, computed tomographic (CT) scans displayed lesions with a central fat density rimmed by a variably radiodense pseudocapsule, leading to the erroneous clinical impression that the lesions were cystic in character. Ultrasonography ruled out a truly cystic tumor by demonstrating internal acoustic interfaces. Magnetic resonance imaging (MRI) in one case showed hyperintense signals in T-1-weighted images, suggesting the presence of fat within the lesional tissue. In the other two cases, CT scans showed reticulated densities accentuating the septa of the orbital fat in the absence of clear-cut circumscription. A potentially useful feature pointing to a neoplasm was bowing of an involved extraocular muscle, which is usually straightened and splinted in either Graves' disease or inflammatory pseudotumor. Histopathologically, two lesions were well-differentiated liposarcomas and three were myxoid liposarcomas, all featuring univacuolar signet ring lipoblasts. Scattered bizarre hyperchromatic mesenchymal cells without prominent lipidization were present in the lesions. None of the patients has experienced regional or distant metastases with follow-ups from onset of 1 to 7 years (mean, 5.2 years); three required orbital exenteration after local recurrence; and two who refused exenteration received only orbital radiotherapy.