Renal disease was observed in two rehabilitated Pacific harbor seals (Phoca vitulina richardsii) from a facility in California (USA). The seals had leukocytosis and high serum phosphorus, blood urea nitrogen and creatinine concentrations. A retrospective study of leptospiral antibody serum titers indicated both seals had elevated titers to Leptospira interrogans serovar grippotyphosa. A third seal, which died about the time when the index cases occurred, also had elevated titers to L. interrogans serovar grippotyphosa. Post mortem histopathologic examination of all three seals showed tubular necrosis consistent with interstitial nephritis; spirochetes were seen within the kidney parenchyma of the third seal. Sea lions (Zalophus californianus) or elephant seals (Mirounga angustirostris) housed near the harbor seals were possible sources of exposure, but local wildlife also could have been responsible.