Potato viruses cause significant potato yield loss world wide. It is important to understand the nature of the potato virus populations present in a geographical region in order to develop appropriate control strategies. A wide-ranging survey of potato viruses in potatoes being grown in the northeastern USA had never been done. A survey of six potato viruses, Potato virus A (PVA), Potato virus M (PVM), Potato virus S (PVS), Potato virus X (PVX), Potato virus Y (PVY), and Potato leafroll virus (PLRV), was conducted in New York and Maine during 2002 and 2003. Leaf samples were tested by ELISA and PVY-positive samples were further tested to determine if a necrotic strain of PVY (PVYN, PVYN:O, or PVYNTN) was present. In both years, PVY and PVS were identified in a majority of the samples, and mixed infections predominated in 83% of the symptomatic leaves in 2002. Of the total 394 PVY-positive samples, three reacted with monoclonal antibody (MAb) 1F5 and caused veinal necrosis (VN) in tobacco. Two of these isolates caused tuber necrosis in the potato cv. Yukon Gold. Three PVY isolates reacted with MAb 1F5 but did not cause VN in tobacco, and two caused VN but did not react with MAb 1F5. Two of the necrotic PVY isolates collected, along with a PVYO isolate, were used to conduct multi-year experiments to determine the impact of PVY strain, potato cultivar, and time of infection on marketable yield and tuber infection efficiency. It was found that final disease incidence in the field could not be used to predict tuber infection, as inoculated plants testing negative in the field produced infected tubers. PVY infection decreased marketable yield, but yield was dependent on the potato cultivar and inoculation time. PVY infected between 25 and 100% of the marketable tubers. Our results suggest that, compared with other isolates, necrotic strains of PVY might be less effectively removed in seed potato production systems and this may explain the emergence of necrotic strains.