A healthy boy developed subacutely progressive quadriparesis, complicated by sudden paraplegia, fever, and meningeal signs, diagnosed as longitudinal myelitis, aseptic meningitis, and conus medullaris infarction and identified as the presenting manifestations of neuropsychiatric systemic lupus erythematosus. Rapid expansion of the conus on serial neuroimaging led to emergent decompressive laminectomy and cord biopsy showing vasculitis and cord infarction. The patient had partial recovery after treatment with high-dose steroids. Increased vigilance is required when pediatric patients develop a similar subacute presentation on the ground of active systemic lupus erythematosus because it may herald the onset of a catastrophic neurological syndrome.