Cerebellar deficient folia, cdf, is a spontaneous autosomal recessive mutation in the mouse with unique pathology; the cerebellar cortex of the cdf/cdf mouse has only 7 folia instead of 10, which is the normal count for the C3H/HeJ strain in which this mutation arose. The cerebellum of the cdf/cdf mouse is hypoplastic and contains mineral deposits in the ventral vermis that are not present in controls. We used an intersubspecific intercross between C3H/HeSnJ-cdf/+ and Mus musculus castaneus (CAST/Ei) to map the cdf mutation to Chromosome (Chr) 6. The most likely gene order is D6Mit16-(cdf, D6Mit3)-D6Mit70-D6Mit29-D6Mit32, which positions cdf distal to lurcher (Lc) and proximal to motor neuron degeneration 2 (mnd2). The definitive visible phenotypes and histopathologies of cdf, Lc, and mnd2 support our mapping evidence that cdf is a distinct gene. The novel pathology of cdf should help elucidate the complicated process of cerebellar folia patterning and development. cdf recombined with mouse atonal homolog 1, Math1, the mouse homolog of the Drosophila atonal gene.