BACKGROUND: Smoking is known to result in a decline in renal allograft function and survival of recipients; however, the effect of smoking on living kidney donors remains unknown. In this study we evaluated the impact of cigarette smoking on renal function of kidney donors. METHODS: Among 1056 donors who underwent nephrectomy, 612 completed the 6-month follow-up protocol and were enrolled in the study. The association of smoking status, including pack-years smoking history, and postoperative renal function was evaluated. RESULTS: Among donors, 68.1% had never smoked, 8% were former smokers, and 23.9% were current smokers. Donors who never smoked were older than former and current smokers (42.3 +/- 11.8, 41.9 +/- 11.1, and 38.3 +/- 10.9 years, respectively; P < .001). There was no difference in preoperative renal function between groups; however, postoperative estimated glomerular filtration rate (eGFR) was lower in former and current smokers than in those who never smoked (64.6 +/- 13.8, 64.7 +/- 12.3, and 67.8 +/- 13.1 mL/min/1.73 m(2), respectively; P = .023). In former and current smokers, pack-years smoking history was negatively associated with pre- and postoperative eGFR (r = -0.305 and -0.435, P < .001), and correlated with postoperative percent eGFR decline (r = 0.248, P < .001). Smoking history was associated with postoperative development of chronic kidney disease (CKD). Especially in former smokers, a smoking history of more than 12 pack-years was strongly associated with development of CKD (odds ratio = 7.5, P = .003). CONCLUSION: Even if they no longer smoke, donors with a smoking history require close observation due to increased risk of CKD development after kidney donation. A detailed pack-years smoking history should be obtained, and smoking cessation strategies should be implemented in kidney donors.