Despite the availability of alternative agents, lithium continues to be the standard against which all mood stabilisers, prescribed for acute and maintenance treatment of bipolar (and, to a lesser extent, unipolar) mood disorders, are compared. As a medication often used on a maintenance basis for a lifelong disorder, the potential for lithium to cause long term organ toxicity has generated appropriate concern. Foremost among these concerns are its renal effects. Lithium adversely affects renal tubular function, causing polyuria secondary to a deficit in urine concentrating ability. This effect is probably progressive for the first decade of lithium therapy, i.e. it correlates with duration of lithium therapy. Although this effect of lithium is probably functional and reversible early in treatment, it may become structural and irreversible over time. In contrast, the effect of lithium on glomerular function is not progressive. Conclusions in this area are hampered by the evidence that patients with psychiatric disorders who are not receiving lithium also show defects in certain aspects of renal function. Despite the generally sanguine data on glomerular function, a very small group of patients may develop renal insufficiency due to lithium (possibly in conjunction with other somatic factors) in the form of interstitial nephritis. However, for the vast majority of patients, the renal effects of lithium are benign. Current strategies for minimising the renal effects of lithium include: (i) assiduously avoiding episodes of renal toxicity; (ii) monitoring serum lithium concentrations in order to achieve optimal efficacy at the lowest possible concentration; (iii) monitoring serum creatinine levels on a yearly basis, getting further medical evaluation when the serum creatinine level consistently rises above 140 mmol/L (1.6 mg/dl); and (iv) possibly administering lithium once a day.