Background and Objective. Timely assessment and prevention of risk factors for the main perioperative complications in elderly patients provide an opportunity to avoid them, decrease mortality, and diminish costs associated with longer hospital stay. The aim of this study was to estimate perioperative factors that could potentially predict the length of stay and to estimate their predictive value using a comprehensive geriatric assessment among elderly patients. Material and Methods. The study population comprised 99 surgical patients aged 65 and more. The patients were followed up until discharge. Study data analysis included questionnaires, anthropometric measurements before surgery, assessment and interviews after surgery, and case histories. Univariate and multivariate logistic regression analysis was performed. Results. Malnutrition was detected in 53.5% of the patients. Postoperative cognitive disorder was documented in 18.2% of elderly patients. The mean length of hospital stay was 10.1 days (SD, 9.14). Multivariate logistic regression analysis revealed that the best predictors for longer hospital stay in elderly patients were malnutrition (OR, 4.2; 95% CI, 1.5–11.8; P=0.007) together with postoperative cognitive impairment (OR, 9.2; 95% CI, 1.0–83.3; P=0.048). The total predictive value of the model was 70.5%. Conclusions. Malnutrition and a postoperative cognitive disorder were independent risk factors for longer hospital stay, while depression, cognitive impairment, functional dependence, and poor physical status were not independently associated with longer hospital stay. A comprehensive geriatric assessment can help assess the risk factors for longer treatment and predict the length of hospital stay, thus enabling the planning of optimal healthcare management of elderly patients.