Cytomegalovirus polyradiculopathy, a late complication of HIV infection, is characterized by lower extremity weakness, urinary retention, and sacral dysesthesias. We describe four patients (mean CD4 T-cell count = 25 cells/mm3) who developed this "infectious cauda equina syndrome." The characteristic cerebrospinal fluid (CSF) findings, notably atypical for a viral infection, included polymorphonuclear leukocytosis (mean white blood cell count = 1512 cells/mm3, 72% polymorphonuclear leukocytes), elevated protein level (mean = 370 mg/dl), and hypoglycorrhacia (mean = 28 mg/dl). Physicians who treat patients with HIV should be familiar with this syndrome because early intervention, prior to microbiologic confirmation, provides the best hope for improving neurologic function.