Leptospirosis has been documented in free-ranging, captive and rehabilitated otariids and phocids on the west coast (U.S.), however, reports of the disease in east coast pinnipeds are rare. Prevalence of the disease is unknown and leptospirosis epizootics have not been documented in east coast pinniped populations. Between January 2003 and December 2008, the University of New England's Marine Animal Rehabilitation Center (MARC) submitted 452 serum samples from four phocid species (C.cristata, H.grypus, P.vitulina, P.groenlandica) to the Oklahoma Animal Disease Diagnostic Laboratory and Athens Veterinary Diagnostic Laboratory for leptospirosis screening. Of 254 animals tested, 130 (51.2%) had low to moderate titers (< 1:800) and ten cases (3.9%) with high Leptospira sp. titers (>1:1600) have been identified in three species of live and dead seals. One P. vitulina examined had high serologic titers to L. canicola while two others had high serologic titers to L. bratislava. Four P. vitulina, two C. cristata, and one H. grypus had high serologic titers to L. hardjo. Two live C. cristata and one live P. vitulina were successfully treated with antibiotics and released. The C. cristata presented with rising titers (1:200-1:400 on intake and 1:3200 on day 14) to L. hardjo, while the P. vitulina was admitted with a high titer (1:1600) to L. hardjo that seroreverted to negative following treatment. Significant clinical signs were not observed in these three cases. A H. grypus presented with symptoms of severe depression, inflamed urogenital opening, congested lung sounds, and anuria. Following unsuccessful treatment with antibiotics, furosemide, and aggressive fluid therapy, the animal was euthanized. Serologic and histopathologic findings were most consistent with leptospirosis. Gross post-mortem findings on some animals with high titers have been suggestive of leptospirosis and have included renal pallor and loss of renule differentiation while others have not shown any gross or pathological findings suggestive of leptospirosis despite high titers. In addition to finding high titers (which are considered positive), moderate and low titers (< 1:800) have been increasing in frequency and new serovars have been observed each year. Heterophilic cross reactivity may be a possibility. However, these findings suggest that while leptospirosis is uncommon in the northeast U.S., surveillance of rehabilitated animals may indicate the frequency of leptospirosis in local pinniped populations and may help predict potential epizootic events.