SUMMARY: CNS lymphoma consists of 2 major subtypes: secondary CNS involvement by systemic lymphoma and PCNSL. Contrast-enhanced MR imaging is the method of choice for detecting CNS lymphoma. In leptomeningeal CNS lymphoma, representing two-thirds of secondary CNS lymphomas, imaging typically shows leptomeningeal, subependymal, dural, or cranial nerve enhancement. Single or multiple periventricular and/or superficial contrast-enhancing lesions are characteristic of parenchymal CNS lymphoma, representing one-third of secondary CNS lymphomas and almost 100% of PCNSLs. New CT and MR imaging techniques and metabolic imaging have demonstrated characteristic findings in CNS lymphoma, aiding in its differentiation from other CNS lesions. Advanced imaging techniques may, in the future, substantially improve the diagnostic accuracy of imaging, ultimately facilitating a noninvasive method of diagnosis. Furthermore, these imaging techniques may play a pivotal role in planning targeted therapies, prognostication, and monitoring treatment response.ABBREVIATIONS: ADC ϭ apparent diffusion coefficient; CBV ϭ cerebral blood volume; CE ϭ contrast enhancement; Cho ϭ choline; CNS ϭ central nervous system; Cr ϭ creatine; DWI ϭ diffusion-weighted imaging; FA ϭ fractional anisotropy; FDG ϭ fluorodeoxyglucose; HAART ϭ highly active antiretroviral therapy; HIV ϭ human immunodeficiency virus; MRI ϭ MR imaging; MS ϭ multiple sclerosis; NHL ϭ non-Hodgkin lymphoma; PCNSL ϭ primary CNS lymphoma; PET ϭ positron-emission tomography; PML ϭ progressive multifocal leukoencephalopathy; rCBV ϭ relative cerebral blood volume; SPECT ϭ single-photon emission CT; SPET ϭ single photon-emission tomography; SWI ϭ susceptibility-weighted imaging L ymphoma of the CNS consists of 2 major subtypes: secondary CNS involvement by systemic lymphoma (the most common) and PCNSL, in which the lymphoma is restricted to the brain, leptomeninges, spinal cord, or eyes, without evidence of it outside the CNS at primary diagnosis.