Patients with indolent lymphoma have a 30% risk of transformation to aggressive large-cell lymphoma. Clinical signs of transformation include elevated lactate dehydrogenase (LDH) levels, B symptoms, hypercalcemia, unusual extranodal sites, and rapid node growth, but these are not definitive. We present 10 patients with indolent lymphoma with solid low-attenuation lesions in the spleen on computed tomographic scans. Six of these patients were diagnosed with transformed lymphoma based on biopsy results. In patients with indolent lymphoma, hypodense lesions in the spleen should be biopsied to rule out transformation. If biopsy is not feasible, empirical treatment for transformed lymphoma is warranted.