OBJECTIVES: To study the risk of nephrotoxicity and the cost of treatment of colistin. METHODS: Patients admitted in ICU with resistant bacterial infections and on colistin for at least seven days were included in the study. They were observed for any change in Glomerular filtration rate and the risk of nephrotoxicity according to the RIFLE criteria after the colistin therapy. The GFR values before the initiation of treatment with colistin were compared with that after the end of regimen. The pre and post treatment GFR values were compared using non-parametric Wilcoxon Signed Ranks test. RESULTS: A total of 30 patients on colistin were observed during the study. The mean age of the patients was 45.47±16.45. The average APACHE II score was 15.87±5.82. There was no significant difference between the GFR of patients before and after treatment with colistin (p=0.130). The average hospitalization cost was 255245.41±138099.29 and the average cost of colistin therapy was 31638.10±12625.90. CONCLUSIONS: This study showed that the nephrotoxic effect of colistin is not significant. There is a need to conduct more studies with a higher sample size to assess the risk of colistin-induced nephrotoxicity. The incidences of nephrotoxicity in the patients studied can be attributed to various other factors such as age, comorbidities etc. The cost of colistin therapy was substantial being more than one-tenth of the total hospitalization cost.