Objectives: To determine whether the potassium citrate therapy is more cost-effective than diet alone. Methods: Effectiveness was rated in terms of 'avoided recurrences' for both interventions. Costs were calculated on the basis of the patient's perspective. The time horizon for this analysis was 3 years, considering the follow-up period for patients included in this clinical trial. Key findings: Those patients who did not show evidence of de novo stone images avoided six recurrence episodes by using potassium citrate and a change in diet. In those patients who showed evidence of de novo stone images with either of the two interventions, we assumed that recurrence would not be avoided (0 avoided recurrences). The cost per individual treated with potassium citrate who showed de novo lithiasis was US$2086 while that for untreated individuals who showed de novo lithiasis was US$1096 under the assumption that recurrence would not be avoided in any case with de novo lithiasis. We calculated a cost-effectiveness (C-E) ratio of US$360 for the intervention with potassium citrate and a C-E ratio of US$3795 for the dietary intervention alone. The incremental C-E ratio indicated that it is necessary to pay US$193 for every additional recurrence avoided with potassium citrate. Conclusions: Intervention with potassium citrate proved to be more cost-effective than changes to diet alone. Two sensitivity tests proved the robustness of these results. © 2011 The Authors. JPHSR © 2011 Royal Pharmaceutical Society.