Purpose: To evaluate the clinical characteristics and investigate the role of surgical antibiotic prophylaxis (SAP) in acute endophthalmitis cases after cataract surgery. Design: Retrospective, consecutive case series. Participants: A total of 126 patients referred to a tertiary center from 2007 to 2015 for acute endophthalmitis after unilateral cataract surgery. Methods: All patients who underwent a vitreous biopsy were included. Clinical and microbiology data were reviewed, and associations with visual outcome were analyzed using multivariate logistic regression. Data regarding SAP via intracameral injection were also retrieved. Main Outcome Measures: Bacterial culture results and visual acuity outcome. Results: Bacterial growth was observed in 92 of 126 cases (73%). Among these positive cultures, 49 (53.3%), 29 (31.5%), and 13 (14.1%) were coagulase-negative staphylococci, other gram-positive, and gram-negative bacteria, respectively. Among the 77 gram-positive strains tested, 76 (98.7%) were vancomycin-sensitive; among the 12 gram-negative strains tested, all 12 (100%) were ceftazidime-sensitive. Best achieved visual acuity outcome was ≥20/40 Snellen in 77 of 114 cases (67.5%). On multivariate analysis, we found an association between visual outcome of worse than 20/40 Snellen and a positive culture of more virulent bacteria (gram-negative and other gram-positive groups) and presentation with light perception or worse, with an odds ratio of 3.3 and 3.0, respectively. A subgroup of 25 cases (19.8%) developed endophthalmitis despite receiving a SAP by cefuroxime at the end of cataract surgery. Conclusions: Two-thirds of the patients in this endophthalmitis cohort experienced a visual outcome of ≥20/40 Snellen. Efficacy of primary treatment with vancomycin combined with ceftazidime is supported by this study. A subgroup treated prophylactically with cefuroxime demonstrated that SAP alone does not prevent endophthalmitis. This highlights the importance of surgical factors in the prevention of postoperative endophthalmitis.