Background: Lithium-induced nephropathy is a known long-term complication, sometimes limiting the use of lithium as mood stabilizer. The aim of this study is to establish the incidence of chronic kidney disease and the rate of decline of renal function in patients using lithium and to identify risk factors. Methods: We selected 1012 patients treated with lithium from the laboratory database of the Antes Centre for Mental Health Care spanning a period from 2000 to 2015. Serum lithium and creatinine concentrations were retrieved and eGFR was calculated using the 4-variable CKD-EPI formula. We calculated the incidence of renal insufficiency and the rate of decline. We compared patients with and without chronic kidney disease (CKD) stage 3 regarding duration of lithium exposure. Results: Incidence of chronic kidney disease was 0.012 cases per exposed patient-year. Average decline of eGFR was 1.8 ml/min/year in patients who developed chronic kidney disease stage 3. Incidence of chronic kidney disease stage 4 was only 0.0004 per patient year. No cases of end stage renal disease were found in this cohort. Odds of reaching chronic kidney disease stage 3 were increased with longer duration of lithium exposure. Conclusions: The use of lithium seems to be related to a higher incidence of chronic kidney disease. Longer duration of lithium exposure significantly increased the risk of renal failure.