Cystic kidney diseases and toxic interstitial nephritis may be complicated by renal tumors. Long-term lithium intake is associated with tubulointerstitial nephritis and renal cysts but to date such an association with tumors has not been determined. We evaluated this in a retrospective study to determine whether lithium-treated patients were at higher risk of renal tumors compared with lithium-free patients with chronic kidney disease (CKD), and to the general population. Over a 16-year period, 14 of 170 lithium-treated patients had renal tumors, including seven malignant and seven benign tumors. The mean duration of lithium exposure at diagnosis was 21.4 years. The renal cancers included three clear-cell and two papillary renal cell carcinomas, one hybrid tumor with chromophobe and oncocytoma characteristics, and one clear-cell carcinoma with leiomyomatous stroma. The benign tumors included four oncocytomas, one mixed epithelial and stromal tumor, and two angiomyolipomas. The percentage of renal tumors, particularly cancers and oncocytomas, was significantly higher in lithium-treated patients compared with 340 gender-, age-, and estimated glomerular filtration rate (eGFR)-matched lithium-free patients. Additionally, the Standardized Incidence Ratio of renal cancer was significantly higher in lithium-treated patients compared with the general population: 7.51 (95% confidence interval (CI) (1.51-21.95)) and 13.69 (95% CI (3.68-35.06)) in men and women, respectively. Thus, there is an increased risk of renal tumors in lithium-treated patients.Kidney International advance online publication, 22 January 2014; doi:10.1038/ki.2014.2.