Personnel at The Marine Mammal Center (The Center) treated 1,446 stranded marine mammals recovered from the central and northern California (USA) coast from 1984 through 1990, including California sea lions (Zalophus californianus), northern elephant seals (Mirounga angustirostris), Pacific harbor seals (Phoca vitulina richardsi), northern fur seals (Callorhinus ursinus), Steller sea lions (Eumetopias jubatus), and Guadalupe fur seals (Arctocephalus townsendi). The primary disease findings in stranded California sea lions were renal disease, renal disease complicated by severe verminous pneumonia, verminous pneumonia, seizures of unknown etiology, and renal disease complicated by severe pneumonia of unknown etiology. Stranded elephant seals included pups, yearlings with dermatological problems, and neonates. Most harbor seals admitted to The Center were underweight and premature pups. Stranded northern fur seals included animals with seizures of unknown etiology and emaciated pups. Stranded Steller sea lions included underweight pups and aged adult females with pneumonia. Two Guadalupe fur seals had hemorrhagic gastroenteritis. Incidental findings at the time of stranding among the six species included verminous pneumonia and pneumonia of unknown etiology, renal disease, internal parasitism, ophthalmologic problems, gastrointestinal disorders, otitis externa, and external wounds.