Purpose: To investigate the influence of corneal collagen crosslinking (CXL) on conjunctival flora.Materials and Methods: Included in this study were 42 patients, all of whom were treated with CXL for progressive keratoconus (KC). Conjunctival swab samples were collected under operating-room conditions immediately before and immediately after the procedure. Samples were quickly immersed in Amies Transport Medium (ATM), transferred to the microbiology laboratory, diluted, and inoculated into three areas each of blood agar, chocolate agar, eosin methylene blue (EMB) agar, and Saboraud-Dextrose agar plates. Inoculated plates were incubated at 35 degrees C for 24-48 h. Preliminary species identification of isolated bacterial colonies was based on catalase and oxidase tests, Gram staining, and colony morphology. Definitive identification of isolates was made with Vitek-II fully automated identification kits.Results: Cultures were positive in 24 (57.1%) preoperative and 10 (23.8%) postoperative samples (p ? 0.05). Microorganisms isolated from preoperative conjunctival samples included coagulase-negative Staphylococcus (CNS) spp. in 23 (54.8%) samples, S. aureus in three (7.1%), Moraxella spp. in two (4.8%), Streptococcus spp. in three (7.1%), Corynebacterium spp, in one (2.4%), Micrococcus spp. in one (2.4%), and Candida spp. in one (2.4%). Microorganisms isolated from postoperative conjunctival samples included CNS spp. in nine (21.4%) samples, S. aureus in one (2.4%), Corynebacterium spp. in two (4.8%), and Acinetobacter spp. in one (2.4%).Conclusions: CXL appears to have a significant impact on conjunctiva flora.