PURPOSE To evaluate the postoperative infection rate after external dacryocystorhinostomy (DCR) without routine systemic antibiotic prophylaxis. METHODS Retrospective review of case notes, including eye casualty attendances, of 77 patients undergoing 82 consecutive external DCR procedures between 22 December 2006 and 31st December 2009 performed by one of the authors (O. M. Durrani) at a single centre (The Birmingham and Midland Eye Centre, United Kingdom). Patients were given topical Maxitrol eye drops (dexamethasone 0.1%, neomycin 3.5 mg and polymixin B sulphate 10,000 units) three times a day for 1 week postoperatively but no systemic antibiotics. RESULTS Postoperative infection occurred in one of 82 cases (1.2%, 95% confidence interval 0.03-6.6%). The one case of infection consisted of superficial wound infection only and was managed with oral antibiotics and resolved with a successful outcome. Thirteen out of 87 cases were performed in patients with recurrent dacryocystitis or mucocoeles; none of these cases were complicated by postoperative infection. CONCLUSIONS Postoperative infection after external DCR without the use of systemic antibiotics is uncommon. Assuming that oral antibiotics are 80% effective at treating postoperative infection, for routine prophylaxis, the number needed to treat to prevent one infection would be 104. Taking the upper confidence limit of 6.6%, the lower limit of the number needed to treat would be 19. The one case of infection was treated successfully with oral antibiotics and resolved with a successful outcome. These results suggest that the routine use of systemic antibiotic prophylaxis in external DCR may not be justified.