High interindividual variability in pharmacokinetics coupled with concentration-effect relationship make sunitinib an ideal candidate for therapeutic drug monitoring (TDM). The feasibility of TDM of sunitinib in patients with metastatic renal cell carcinoma (mRCC) was evaluated in this prospective observational study. Seventy patients with mRCC treated with sunitinib 50mg OD were enrolled. Total trough levels (TTL) of sunitinib and N-desethyl sunitinib were measured between days 10-14 of cycle 1. The discriminatory potential of TTL of sunitinib for the prediction of responders and occurrence of grade ≥3 toxicity was determined using receiver operating characteristic (ROC) curve. Threshold concentrations obtained from ROC analysis showed that TTL ≥60.75ng/mL was associated with higher response rates and TTL ≥82.3ng/mL was associated with higher incidence of grade ≥3 toxicity compared with lower exposures (31/34 versus 5/12, P=0.001 and 9/24 versus 4/36; P=0.024 respectively). More than 50% of patients in our cohort attained TTL outside the optimal range of 60.75-82.3 ng/mL demonstrating the feasibility of TDM.