Patients with diabetes mellitus (DM) are prone to infection because glucose in the skin, urine, mucous membranes, and tears promotes growth of microorganisms. Conjunctival flora develops soon after birth, and some saprophytic conjunctival flora play a pathogenic role when immune function is compromised, which can lead to serious infection. DM is one condition that may compromise immune status. In lacrimal function tests of DM patients, a decrease in breakup time (BUT) of lacrimal film and a decrease in Schirmer's test results were seen. In the present study, conjunctival flora in patients with DM was compared with that in controls with regard to type and duration of diabetes and results of lacrimal function tests. Seventeen patients with type 1 DM (n=34 eyes), 66 patients with type 2 DM (n=132 eyes), and 50 control subjects (n=100 eyes) were included. The control group consisted of age-matched patients with no ophthalmologic problems other than refractive error. Glycosylated hemoglobin values were measured with highpressure liquid chromatography with the Hi-AUTOA1c analyzer (Kyoto Daiichi Kagatu Co., Ltd., Kyoto, Japan). Type and duration of diabetes and demographic data were recorded, and routine ophthalmologic examinations were performed; the BUT of lacrimal film was determined, and the results of Schirmer's test were assessed. Microbiologic sampling was performed twice for both eyes with sterile cotton swabs. One sample was incubated in 2 mL of brain-heart infusion broth agar; the other was incubated for the presence of fungi in Sabouraud dextrose agar. Colony morphology, hemolysis, and Gram's stain, as well as catalase, oxidase, and coagulase tests were performed. No growth was observed in 12 of 17 patients (35.4%) with type 1 DM, 28 of 66 patients (21.2%) with type 2 DM, and 25 of 50 control subjects (50%). Staphylococcus epidermidis (11.79%) and Staphylococcus aureus (11.7%) were the most frequently isolated organisms in the type 1 DM group, and S epidermidis (24.2%) and S aureus (21.2%) were the predominant organisms in the type 2 DM group. In control subjects, S epidermidis (22%), S aureus (12%), and Corynebacterium spp (10%) were the most frequently isolated organisms, and the number of eyes with growth of S aureus was significantly higher in the type 2 DM group than in the other groups (P<.01). Patients with diabetes are more prone to postoperative endophthalmitis than are nondiabetics, and preoperative application of antiseptic or antimicrobial agents to the conjunctiva may not sterilize the area. Impaired integrity of the posterior capsule may also increase the risk of endophthalmitis. Postoperative endophthalmitis is usually associated with gram-positive organisms (75%-80%); gram-negative organisms (15%-29%) and fungi (3%-13%) account for a smaller number of cases. A high rate of resistance to penicillin, ampicillin, and tetracycline was observed in S aureus isolates, although resistance to vancomycin was absent, rendering this molecule the most effective therapeutic option. In this study, S epidermidis and S aureus were the 2 most frequently isolated organisms in patients with DM. It is concluded that the conjunctival flora in diabetic subjects differs from that in nondiabetic subjects. This should be considered preoperatively and postoperatively, and prophylactic and postoperative treatment should be administered accordingly to diabetic patients.