OBJECTIVE: To evaluate the effect of prophylactic therapy on gout flare during urate lowering treatment. METHODS: We retrospectively examined the data derived from 59 patients who had been treated with allopurinol for more than six months after stopping prophylactic medication at our rheumatology clinic. Demographic data (age, sex, disease duration, tophi and comorbidity), clinical and laboratory features, including presence of gout flare during urate lowering treatment, dose of allopurinol, serum uric acid level and creatinine clearance at initiation and six months later, were collected. For the subgroup analysis, the same data were collected in 46 patients who had been followed up at one year after stopping prophylactic medication. RESULTS: Twenty-eight patients among 59 (47.4%) had experienced at least 1 gouty attack during urate lowering therapy. The mean duration of prophylactic medication was not different between the flare group (3.8 months) and the non-flare group (5.9 months, p=0.617). Six months later, the mean serum uric acid level was 6.3 mg/dL (6.1 mg/dL vs. 6.5 mg/dL). According to the duration of prophylactic treatment (<6 months, > or =6 months), there were more frequent flares in the <6 months group than in the > or =6 months group (51.2% vs. 38.9% in the six month follow-up group, 70.6% vs. 50% in the one year follow-up group). CONCLUSION: Prophylactic medication for more than six months could be a favorable factor for the prevention of recurrent gout flare during urate lowering treatment.