OBJECTIVES: Analyze the cost-effectiveness of the prophylaxis (n-acetylcysteine 1200mg 4 oral-doses+1/6M bicarbonate 500ml IV) of the contrast-induced nephropathy (CIN) at risk patients. The CIN is usually reversible, but may affect 50% of patients with some risk factors (diabetes, age...) and may favor the progressive renal damage. METHODS: Retrospective observational study. The population were patients  candidates at prophylaxis protocol CIN in a university hospital during 2012 (5142 patients). We calculated a sample size of 115 patients for a confidence level of 90%, an error of 7.5% and a frequency of CIN equal 40% . CIN was considered as the relative elevation of serum creatinine greater than or equal to 25% during the 48 hours after the test. For the economic analysis were used acquisition-costs of drugs, and the hemodialysis costs described by Lorenzo et al (Nephrology2010,30(4):404-412). We consider, according to literature that at least 35% of risk patients affected by NIC would require a hemodialysis session. RESULTS: Of the patients who received prophylaxis, 3 had CIN and 93 no. Of those who received no prophylaxis 5 had CIN, and 14 no. We did a Fisher Test being the difference in favor of the protective effect of the protocol statistically significant (p <0.01). The prophylaxis would have prevented 25.26 CIN. The prophylaxis costs per patient were € 2.29 . The cost of a hemodialysis sessions was € 423. Then € 220.42 has been invested to avoid a minimum of € 3739.74 on hemodialysis. (16.9 € savings per euro spent on prophylaxis. Each avoided NIC had cost € 8.73.) CONCLUSIONS: The economic analysis is difficult because of the diversity of data about CIN. We chose a cost-minimization model, considering minor treatment needs found in the literature. In any case this prophylaxis is highly cost-effective and should be considered before introducing other methods.