Abstract. Introduction. This case report illustrates the relatively rare occurrence of a urinoma masquerading as an abscess in a patient with refractory recurrent non-Hodgkin's lymphoma. Although urinomas have been reported after urinary instrumentation, our case was confounded by a concurrent pleural effusion, an immunocompromised host, and clinical appearance and subsequent incision and drainage that was consistent with an abscess. Although not the first case reported in the literature, the constellation of findings in our patient demonstrates the importance of including urinoma in the differential diagnosis of patients with flank mass. Case presentation. Here we report a case of a retroperitoneal fluid collection found in an immunocompromised 65-year-old Caucasian woman. She had recurrent non-Hodgkin's lymphoma and was neutropenic when the collection was found. Drainage of the fluid demonstrated infection, but the case was complicated by increasing fluid production and the development of an ipsilateral pleural effusion. Despite pleural drainage, the abscess output continued to be high. A computed tomography scan demonstrated fluid collection around the renal calices suggestive of rupture; analysis of the fluid was suggestive of a urinoma. The etiology, pathogenesis, and treatment of urinomas in such patients are discussed. Conclusions: Urinomas can present in patients who have had urinary tract instrumentation or trauma, but can occur in other hosts. Patients with hematologic malignancy can develop malignant or sympathetic pleural effusions and are at risk for skin and soft tissue infections. Clinicians caring for immunocompromised patients, particularly hematologists, oncologists, and transplant clinicians, should be aware of this potential complication because rapid identification and attempt at correction are important to optimize outcome. © 2013 Vaidya and Swetz; licensee BioMed Central Ltd.