A 7 yr old female spayed mixed-breed dog was presented for a 1 wk history of neck pain and pelvic limb weakness. Examination revealed nonambulatory paraparesis and thoracolumbar hyperesthesia. MRI revealed extensive intramedullary T2-weighted/short tau inversion recovery hyperintensity and diffuse severe T1-post contrast meningeal enhancement of the thoracolumbar spinal cord. An L5-L6 cerebrospinal fluid sample revealed a suppurative pleocytosis (81% neutrophils, total protein 4362.5 mg/dL and nucleated cell count 352,000/μL). While awaiting the results of infectious disease testing, the dog was treated for suspected meningoencephalitis of unknown etiology with corticosteroids, cyclosporine, and a cytarabine arabinoside infusion. The dog neurologically declined and was started on broad-spectrum antibiotics. The dog continued to decline despite antibiotics, and infectious disease titers subsequently revealed serum antibody positivity for blastomycosis. The dog was then referred to a multispecialty referral hospital and was treated with amphotericin B followed by fluconazole. Prednisone was continued at anti-inflammatory doses. Urine blastomycosis antigen testing was submitted for subsequent disease monitoring but was negative. Five months after presentation the dog was clinically doing well with no identifiable neurologic deficits. This case demonstrates that neurologic blastomycosis may have negative urine antigen concentrations in some dogs and that other diagnostic modalities should be pursued when central nervous system fungal disease is suspected.