Cerebellar hypoplasia in cats is caused most commonly by an in utero or perinatal infection with feline panleukopenia virus (parvovirus). Cerebellar hypoplasia has been reported infrequently in dogs, but no viral etiology has been identified to date. DNA was extracted from archival, paraffin-embedded, cerebellar tissue from 8 cats and from 2 canine littermates with cerebellar hypoplasia, 2 canine littermates with cerebellar cortical abiotrophy, 6 dogs with congenital cerebellar vermal defects, 1 dog with congenital hydranencephaly, and 15 dogs and cats with various encephalitdes. The DNA extracted from each cerebellum was subject to polymerase chain reaction (PCR) amplification by 3 primer pairs specific for parvovirus DNA. Sequence analysis of PCR products from each of the 8 cats and 2 dogs with cerebellar hypoplasia confirmed their identity with parvoviral DNA. The 6 dogs with cerebellar vermal defects, 2 dogs with cortical abiotrophy, 1 dog with congenital hydranencephaly, and all control samples were PCR negative for parvovirus. Parvoviral structural proteins were not identified by immunohistochemistry in either dog with cerebellar hypoplasia. This study shows that parvoviral DNA can be amplified from feline and canine archival brain tissue and that cerebellar hypoplasia in dogs might be associated with in utero parvovirus infection.