BACKGROUND: The economic impact of therapeutic non-adherence in chronic diseases has rarely been examined using qualitative standards for economic evaluation. This study illustrates the impact of non-adherence on the cost utility of renal transplantation versus haemodialysis from the societal perspective and examines the scope for adherence-enhancing interventions. METHODS: Long-term costs and outcomes in adherent and non-adherent renal transplant patients were simulated in a Markov model. The cost (euros, year 2000 values) and outcome data that were imputed in the model were derived from a prospective study in renal transplantation candidates performed in 2002. Probabilities of adverse events, graft rejection, graft loss and death in adherent and non-adherent renal transplant patients were derived from literature. RESULTS: Compared with dialysis, renal transplantation offers a better outcome in both adherent and non-adherent patients. Lifetime costs after transplantation in the adherent patient group are higher than lifetime dialysis costs and lifetime costs in the non-adherent patient group, mainly because adherent patients live longer after transplantation. Long-term outcomes after transplantation are better for adherent than for non-adherent patients. The mean cost per QALY gained in adherent patients relative to non-adherent patients was euro 35 021 per QALY (95% CI 26 959, 46 620). CONCLUSION: Compared with established healthcare interventions, such as haemodialysis, renal transplantation can be considered a cost-effective therapy for patients with end-stage renal disease, even if patients are non-adherent after transplantation. The low incremental cost per QALY calculated in this model for adherent renal transplant patients, suggests there may be scope for adherence-enhancing interventions (provided that such interventions with a sufficiently high effectiveness exist or can be developed). As the findings are based on simulated long-term costs and outcomes, they should not be considered as precise estimates of the impact of non-adherence. This study is rather meant as an illustration of how non-adherence may impact on the results of cost-effectiveness analyses.