Forty-six patients treated with lithium for an average of 8 yr participated in a follow-up study involving a kidney biopsy. The results were compared with renal biopsy specimens from an age-matched group of controls never treated with lithium. The average number of totally scelerotic glomeruli and atrophic tubuli was higher in lithium-treated patients. The histopathological changes showed significant correlations with lithium dosage schedule. Both the proportions of sclerotic glomeruli, atrophic tubuli and focally distributed interstitial fibrosis were higher in patients receiving their lithium two or three times a day than when lithium was given in a single daily dose.