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Lithium (Li+) salts are widely used to treat bipolar mood disorders. Recent trials suggest a potential efficacy also in the treatment of amyotrophic lateral sclerosis and Alzheimer’s disease. Li+ is freely filtered by the glomerulus and mainly reabsorbed in the proximal convoluted tubule. Reabsorption in the distal nephron becomes significant under sodium-restricted conditions. Nevertheless, the distal nephron is greatly affected by Li+ even under normal sodium intake. Polyuria, renal tubular acidosis and finally chronic renal failure are the most frequent adverse effects. The occurrence of an overt nephrogenic diabetes insipidus (NDI) limits Li+ usage and imposes suspension. The molecular mechanisms of Li+-related urinary concentration defect involve a dysregulation of the aquaporin system in principal cells of the collecting duct. ENaC is crucial as the entry route for intracellular Li+ accumulation. The basolateral exit route is not clearly identified, but some evidence suggests Na+/H+ exchanger 1 (NHE1) as a potential candidate. Li+ promotes polyuria mainly counteracting the intracellular vasopressin signaling. An additional role of the inner medullary interstitial cells and PGE-2 pathway has to be considered. The GSK3β cascade is also regulated by Li+. GSK3β inhibition could lead not only to the polyuria, but also to the Li+-dependent proliferative effect on principal cells. Cellular reorganization of the collecting duct and microcysts are the main pathological findings during Li+ treatment. Their relationship with the urinary concentration defect and an eventual Li+-induced ciliopathy has to been investigated. Li+-induced NDI has been a matter of …