Clinical or subclinical malnutrition occurs in 30% to 70% of patients with advanced heart failure and increases the risk of postoperative adverse events. The main objective of this study was to assess the nutritional status of patients prior to left ventricular assist device (LVAD) implantation using different methods of malnutrition assessment and to evaluate the relationship between nutritional status and postoperative adverse events. A retrospective cohort study included 120 patients aged 26–74 years referred for LVAD surgery. Preoperative nutritional status (NRS-2002—Nutritional Risk Score 2002, NRI—Nutritional Risk Index, PNI—Prognostic Nutritional Index; TLC—total lymphocyte count) and postoperative adverse events were assessed. Moderate to severe malnutrition was found in 55.8%, 43.3%, 40.0%, and 20% of all patients, respectively, according to the PNI, NRI, TLC, and NRS-2002 scores. Patients with a TLC < 1200 cells/m3 had a higher risk of postoperative acute renal failure [hazard ratio (HR): 2.5; 95% confidence interval (95% CI): 1.01–6.3] and death during the observation period [HR = 2.1; 95% CI: 1.2–3.5]. Moderate to severe malnutrition was also associated with a significantly increased risk of in-hospital death [for the NRI score, HR = 4.9 (95% CI: 1.1–22.0); for the PNI score, HR = 5.0 (95% CI: 1.1–22.3)]. In conclusion, moderate to severe malnutrition prior to LVAD implantation has been identified as a risk factor for postoperative acute renal failure and mortality. Assessment of nutritional risk may improve patient selection and early initiation of nutritional support.