BACKGROUND: Malnutrition is a frequent condition among hospitalized patients and a factor of increased risk of postoperative complication. OBJECTIVE: This study aimed to evaluate the impact of malnutrition on phase angle (PA), body water distribution and clinical outcomes in surgical patients with colorectal disease. METHODS: This retrospective study was performed in a tertiary hospital with 40 patients admitted electively. In the preoperative evaluation, global subjective assessment and bioelectrical impedance analysis were performed to determine nutritional status, PA, extracellular water (ECW), intracellular water (ICW) and total body water (TBW). In postoperative evaluation, the length of hospital stay and severe complications, according to Clavien-Dindo classification, were determined. The optimal PA cutoff for malnutrition screening was determined by ROC curve analysis. RESULTS: Seventeen (42.5%) patients were diagnosed as malnourished and 23 (57.5%) as well-nourished according to global subjective assessment. Twelve (30.0%) patients developed severe complications. The malnourished group presented lower values of serum albumin (P=0.012), hematocrit (P=0.026) and PA (P=0.002); meanwhile, ECW/ICW (P=0.019) and ECW/TBW (P=0.047) were higher. Furthermore, 58.8% of malnourished patients developed severe postoperative complications compared to 8.7% of well-nourished. Malnutrition was independent predictor of severe postoperative complications (OR=15.00, IC: 2.63-85.68, P=0.002). The optimal PA cutoff obtained was 6.0º (AUC=0.82, P=0.001), yielding sensitivity, specificity, positive predictive value and negative predictive value of 76.5%, 87.0%, 81.3% and 83.4%, respectively. CONCLUSION: Malnutrition was an independent predictive factor for severe complications in patients underwent to elective major coloproctological surgery. Besides that, malnutrition was associated with lower PA values and greater ratio of ECW. The PA provided great accuracy in nutritional screening, implying a useful marker of malnutrition.