Corynebacterium species are considered nonpathogenic in canine dermatitis; however, potential clinical significance has been demonstrated in canine otitis externa and from a dog bite wound in a human. Objectives of this study were to identify the predominant Corynebacterium species present in lesions of canine dermatitis, assess pathogenic role, determine antimicrobial susceptibility, and evaluate clinical response. Of 37 isolates identified as Corynebacterium, 31 were Corynebacterium auriscanis . Most Corynebacterium isolates were susceptible to chloramphenicol (97%), tetracyclines (92%), and amikacin (89%); isolate susceptibilities to β-lactams, trimethoprim-sulfonamides, and fluoroquinolones were <50%. Most cultures grew mixed populations of bacteria; C. auriscanis was the only organism isolated in three patients. At recheck, 2-8 wk after initial presentation, pleomorphic rods were absent or significantly decreased in all patients. Two of three C. auriscanis isolates were obtained in pure culture and were evaluable, meaning patient had an initial exam and recheck examination. Both patients were already on antimicrobials to which C. auriscanis was resistant in vitro. Both improved after doxycycline administration. C. auriscanis may act as an opportunistic pathogen in canine dermatitis and may not respond to antimicrobial therapy based on susceptibilities for other organisms in mixed infections. Occasionally, Corynebacterium isolated alone may be pathogenic.