A 3-year-old male, hybrid mallard duck (Anas platyrhynchos) was presented with a 2-year history of progressive, ascending paresis and paralysis. On presentation, the bird was in sternal recumbency and displayed intermittent focal seizures and intention tremors. Proprioceptive deficits and absent withdrawal reflexes were observed in both pelvic limbs, wing extension was limited, and reflexes were diminished bilaterally. Other findings included emaciation and dehydration. Results of a complete blood count and plasma biochemical analysis revealed anemia, hypoproteinemia, hypoglycemia, and hyperuricemia. Radiographs were unremarkable and results of an Aspergillus antibody were weakly positive. The duck went into cardiopulmonary arrest and died approximately 1 hour after initiating treatment with intravenous crystalloid fluids. A postmortem diagnosis of neuronal ceroid lipofuscinosis (NCL) was made based on the presence of neuronal granular cytoplasmic material that was autofluorescent and stained with periodic acid–Schiff and Luxol fast blue. To our knowledge, this is only the second case report of NCL in an avian species and the first in waterfowl.