PURPOSE To assess the outcome of medical treatment with oral clarithromycin in patients with chronic post-surgical endophthalmitis. METHODS This prospective study was performed between January 1999 and September 2003. Patients with a diagnosis of chronic post-surgical endophthalmitis of bacterial etiology were included. All received 500 mg of oral clarithromycin twice a day for 14 days. The initial and final visual acuity, etiology, post-surgical time of presentation, treatment-delay time, and follow up were recorded. According to the treatment results, patients were distributed into 3 separate groups: 1) complete response, 2) partial response, 3) no response. Data from these groups were compared by means of the Student's t test and Fisher exact test, depending on which was considered most suitable. RESULTS Fifteen cases of chronic endophthalmitis (11 of Propionibacterium acnes, 4 of Staphylococcus epidermidis) were diagnosed. A complete response was observed in 4 cases, partial response in 4 cases, and no response in 7 cases. Final visual acuity greater than 0.5 was significantly more likely in the complete response group when compared with the no response group (Fisher exact test = 0.0454, p=0.05), however, the same comparison between the complete response group and the partial response group was not significant. CONCLUSION Medical treatment with oral clarithromycin could be useful in some patients with chronic post-surgical endophthalmitis.