BACKGROUND: The long-term risk of chronic kidney disease (CKD) in lithium (Li)-treated patients has been well established in the recent years. METHODS: We have evaluated GFR and serum calcium monitoring in 1179 Li-treated outpatients from an ambulatory laboratory database study. This has been performed in a single private laboratory in Paris from February 1997 to December 2004. Estimated GFR (eGFR) has been calculated using the abbreviated MDRD equation. RESULTS: During an 8-year period, 695 patients (59%) had at least one serum creatinine measurement, whereas 484 had no creatinine measurement. The former group had also more frequent serum Li measurements. Mean serum lithium levels, were similar in both groups, 0.65 mmol/l vs 0.62 mmol/l. The percentage of patients with CKD stage 3 (eGFR 30-59 ml/min/1.73 m(2)) were 36%, 53%, 73% and 77%, and with CKD stage 4, 3%, 5%, 5%, 8% in patients aged 20-39, 40-59, 60-69, and > or = 70 years respectively. There was no significant rise in creatinine measurements (from 35% of the patients with at least one serum creatinine in 2003 to 39% in 2004; P = 0.66) despite intervention to intensify GFR monitoring by physicians. Serum calcium was tested at least once in 212 patients (18%) of whom 15 (7%) were found with hypercalcaemia. CONCLUSION: A very high percentage of Li-treated outpatients have low eGFR. GFR monitoring is neglected in these patients, the majority of whom are no longer attending specialized clinics. Hypercalcaemia is less common but serum calcium monitoring is even more neglected. Ambulatory laboratory database surveillance provides a powerful means to contribute to CKD screening and monitoring.