Four cases of bacterial endophthalmitis occurred after more than 2,800 closed vitrectomies. Despite vigorous antibiotic therapy, all four eyes were lost. The poor outcome seems to result from difficulties in diagnosing this condition in its early stages. Important clinical indications, such as orbital pain, corneal edema and infiltrate, excessive intraocular inflammatory reaction, hypopyon, and diminished fundus reflex, are often masked by the usual postoperative course. According to our study, the incidence of endophthalmitis after closed vitreous surgery is 0.14%. Three of the four patients with endophthalmitis were diabetic. Our clinical findings are compared with those in the four other cases reported in the literature.