The complete genomic sequence of an isolate (PRI-509) of the C strain of Potato virus Y (PVY(C)), which was originally isolated from potato in 1938, was elucidated. The genomic RNA of PRI-509 consists of 9699 nucleotides, with the capacity to encode a polyprotein of 3061 amino acids with a molecular mass of 337 kDa.This is the first full-length sequence of a PVY (C) isolate from potato that belongs to the C1 phylogenetic subgroup, which was previously thought to exclusively contain non-potato isolates.