A free-ranging juvenile fisher (Martes pennanti) with ataxia, lethargy, stupor, and intermittent, whole-body tremors was examined postmortem. Microscopically, the fisher had protozoal meningoencephalitis caused by Sarcocystis neurona, which was confirmed by immunohistochemistry, polymerase chain reaction (PCR) and restriction fragment length polymorphism testing, and genetic sequencing. Sarcocysts found in the skeletal muscle of the fisher were negative for S. neurona by PCR, but were morphologically similar to previous light and electron microscopy descriptions of S. neurona. This is the first report of clinical neural S. neurona infection in a fisher.