OBJECTIVE: Hyperphosphataemia in patients with end-stage renal disease can affect mineral homeostasis, resulting in secondary hyperparathyroidism, osteodystrophy and vascular calcification. Several phosphate binders are currently available; however, they are associated with a range of side effects. Lanthanum carbonate is a new phosphate binder that effectively controls serum phosphorus levels. METHODS: We assessed the cost effectiveness of lanthanum carbonate as a second-line treatment for patients inadequately controlled using maximum doses of calcium-based phosphate binders as recommended by the National Kidney Foundation (USA). Quality-adjusted life years (QALYs) gained were used as the measure of effectiveness, and the standard for cost per QALY gained adopted as the threshold for cost effectiveness was that of the National Institute for Clinical Excellence (NICE) in the UK. The clinical pathways model used to estimate cost effectiveness had the following structure: 1)Patients who failed on calcium carbonate received a trial period on lanthanum carbonate; 2)Those who succeeded on lanthanum carbonate continued to receive it; 3)Those who failed on lanthanum carbonate switched back to calcium carbonate; 4)Serum phosphorus levels were estimated for each subgroup using clinical trial results; 5)Implied relative risk of mortality (based on Block et al) was applied to USRDS survival data and thus QALYs gained were calculated; and 6)Treatment costs were attached to each pathway. RESULTS: The results demonstrate that lanthanum carbonate is cost effective at conventional NICE thresholds for patients whose phosphorus level remains above 6.6 mg/dL (2.1 mmol/L) when treated with calcium carbonate. CONCLUSION: For patients who achieve a phosphorus level below 6.6 mg/dL on calcium carbonate, lanthanum carbonate is unlikely to be cost effective on reasonable assumptions about its price. Lanthanum carbonate becomes progressively more cost effective with increasing phosphorus levels for patients treated with calcium carbonate.