OBJECTIVE Lymphomatous ovarian involvement is an uncommon event, both for primary and systemic lymphoma. It presents different diagnostic and therapeutic implications from the more common ovarian epithelial cancer. We investigated the role of imaging techniques in the diagnosis of these lesions. METHODS Eight patients, aged 13 to 70 years (mean: 47) were selected from all the CT examinations performed from 1986 to 1996 to assess the most typical imaging patterns. All the patients underwent a CT examination, with contiguous 8 or 10 mm thick slices and thin (4-5 mm) detailing slices; iodinated contrast agents were administered in 6 cases. Six patients were also examined with sonography (US). Lastly, 3 patients underwent a MR examination, 2 of them with paramagnetic contrast agent. RESULTS All the patients were affected with non-Hodgkin lymphoma (6 diffuse lymphomas--1 lymphoplasmocytoid, 2 Burkitt, 1 large cells, 1 large and oat cells, 1 immunoblastic large cells, 2 follicular large cells lymphomas). Two patients had primary lesions and the other 6 had a systemic lymphoma; ovarian involvement was bilateral in 6 cases. The lesion size always exceeded 5 cm. Ascitis was present in only one case. The US patterns of the lesions were aspecific, homogeneous and hypoechoic; color Doppler US showed mild vascularization. CT showed clear-cut lesions, hypodense and with mild contrast enhancement in all cases. Spin-echo MRI showed homogeneous masses which were moderately hypointense on T1-weighted images and slightly hyperintense on T2-weighted images. Gd-T1-weighted images showed mild enhancement. CONCLUSIONS The differential diagnosis of ovarian primary lymphoma is usually made with ovarian epithelial neoplasms, which normally have a complex structure with cystic or necrotic areas and solid components usually enhancing after contrast agent administration. Also sarcomas and, in children, neuroblastomas usually have an inhomogeneous structure. In ovarian involvement with systemic lymphoma the concrurrent finding of adenopathy can help the diagnosis. CONCLUSIONS Despite the absence of typical imaging patterns, we emphasize the importance of considering ovarian lymphoma in the differential diagnosis of ovarian cancers, especially if bilateral and homogeneous, without ascitis. These findings, uncommon in ovarian epithelial tumors, can help to make the correct diagnosis.