To find an optimal range of urate concentrations wherein the risk of attacks during the initial 6 months of treatment is minimized, data from 350 gouty patients treated with anti-hyperuricemic drugs were retrospectively analyzed. We determined the optimal range of urate concentrations to be 4.6-6.6 mg/dl. If urate concentrations were within this range, the risk ratio of an attack as opposed to outside of the range was 0.705 (95% confidence interval, 0.629-0.791). The increase (or decrease) in urate concentration in one month associated with minimal risk of gouty attacks was also determined. The lowest risk ratio of attack (0.451) occurred at a range of -0.1 to 0.6 mg/dl/month increase in urate concentrations (95% confidence interval, 0.310-0.655). In conclusion, we propose that urate concentrations during the initial 6 months of anti-hyperuricemic therapy should be maintained within a range of 4.6-6.6 mg/dl, and reduction in the urate concentrations during treatment should be as slow as possible.