An elderly man developed endophthalmitis 1 week after cataract extraction and lens implantation. Intraocular samples were collected and the patient received intravitreal vanco-mycin and ceftazidime, and topical tobramycin. A Gram stain of vitreous humour revealed spindle-shaped Gram-negative bacilli. He was then given systemic clindamycin and topical ofloxacin. Capnocytophaga canimorsus, a member of the oral flora of dogs and cats, was cultured after 3 days. The infection resolved leaving the patient with a visual acuity of 6/60. An attempt was made to culture the organism from the mouth of the patient's pet dog. This was unsuccessful and the source of the infection remains unknown.