Background Lithium can influence calcium homeostasis resulting in changes in parathormone set point and renal calcium handling. The clinical significance of these changes in older patients is unknown. The objective of this study was to investigate the possible association between duration of lithium treatment and corrected calcium, parathormone and 24‐h urinary calcium excretion in older psychiatric patients corrected for renal function and vitamin 25OH D and also to estimate the point prevalence of hypercalcemia and raised parathormone. Methods A cross‐sectional study of psychiatric outpatients visiting a specialized facility for older patients treated with lithium was performed. Patients underwent a comprehensive assessment and blood and urine testing. Potential confounders of calcium homeostasis were recorded. On the basis of the duration of lithium treatment, patients were divided into four groups. Results One hundred eleven patients were included, mean age 75.2 years. There was no significant association between the duration of lithium treatment and corrected calcium, parathormone and 24‐h urinary calcium excretion. The point prevalence of hypercalcemia was 2.7% and 47.8% for raised parathormone. There was an unexpected but significant negative association between the duration of lithium treatment and vitamin 25OH D, with 76.9% vitamin 25OH D deficiency (<50 nmol/L) in the group using lithium for more than 10 years. Conclusions No association was found between duration of lithium treatment and calcium parameters in older psychiatric outpatients, but there was a high prevalence of raised parathormone and an unexpected negative association between duration of lithium treatment and 25OH D. Copyright © 2013 John Wiley & Sons, Ltd.