BACKGROUND/AIM: Sunitinib is used for the treatment of metastatic renal cell carcinoma (mRCC). Asian patients, including Japanese, tend not to tolerate long-term sunitinib therapy of 50 mg p.o. once daily for 4 weeks, followed by 2 week off treatment due to severe adverse events at this dosage level. The aim of this retrospective study was to investigate the optimal dose of sunitinib for long-term continuation in Asian patients with mRCC. PATIENTS AND METHODS: The study cases were 50 patients with mRCC who were treated with sunitinib between June 2008 and December 2017. Risk analysis for "unacceptable" adverse events (depending on the physician, ranging from grade 2 to ≥ grade 3) leading to discontinuation of sunitinib was determined by time-dependent Cox proportional hazard regression analysis. RESULTS: A total of 54 unacceptable adverse events leading to discontinuation occurred. Multivariable analysis indicated that a sunitinib dose of ≤ 37.5 mg/day significantly reduced the risk of discontinuation due to adverse events in comparison with 50 mg/day [hazard ratio (HR) 0.08, 95% confidence interval (CI) 0.03-0.21, p < 0.001). The progression-free survival (PFS) with a sunitinib dose ≤ 37.5 mg/day was longer than that associated with a dose of 50 mg/day, albeit not to a statistically significant degree (120 days for ≤ 37.5 mg/day vs 41 days for 50 mg/day, HR 0.39, 95% CI 0.10-1.44, p = 0.157). CONCLUSION: Our findings suggest that the optimal dose of sunitinib for Asian, including Japanese, patients with mRCC is ≤ 37.5 mg/day.