Multiple organ failure syndrome and acute renal dysfunction share many of physiologic factors involved in their development. Recent studies correlate the susceptibility to organ dysfunction in critically ill patients with genetic inheritance. Many of them consider ACE gene could be a possible candidate to elucidate a genetic predisposition or a genetic risk factor. We aimed to examine the effects of I/D and -262A > T ACE polymorphisms in the renal function in severely ill southern Brazilians patients. A multi-organic worldwide known failure score, the SOFA (sequential organ failure assessment), was used to determine the basal health state at first day (ICU admission). Considering admission SOFA score and trend of renal function (measured by daily renal SOFA scores, with daily measure of serum creatinine and diuresis), we hypothesize that ACE polymorphisms could influence in the trend of renal function in ICU patients. A total of 153 critically ill adult patients (79 men) were included in this study. We monitored the patients daily during their entire ICU and post-ICU (hospital) stay (measured from the ICU admission day to a maximum of 224 days). We observed progression to renal failure (SOFA scores 3 and 4) in first seven days of ICU stay and need for dialysis. The general genotypic frequencies in our sample were II = 0.17; ID = 0.46; DD = 0.37 and AA = 0.30; AT = 0.55; TT = 0.15, and the allelic frequencies were I = 0.40; D = 0.60 and A = 0.56; T = 0.44. This is the first study to verify the influence of I/D and -262A > T ACE polymorphisms in acute renal dysfunction among critically ill patients. No significant association was found between genotypes or allele frequencies and the trend of the renal function. The I/D and -262A > T ACE polymorphisms have no significant impact on the trend of renal function during the first week of ICU stay, neither any influence in mortality in critically ill patients.