AIM:To investigate the role of sex hormones in the early postoperative complications of gastrointestinal diseases. METHODS:A total of 65 patients who underwent operations for gastric and colorectal diseases (mainly malignant diseases) were included in the study. Peripheral venous blood samples were collected at different times for analysis of estradiol, testosterone and progesterone. The only study endpoint was analysis of postoperative complications. RESULTS:Patients of both sexes were uniform but postoperative complication rate was significantly higher in female patients (P = 0.027). There was no significant association of estradiol and progesterone with postoperative complications. Testosterone levels in complicated patients were significantly lower than in uncomplicated patients (P < 0.05). Area under the receiver operating characteristic curve showed that a lower value of testosterone was a predictor for higher complication rate (P < 0.05), and a lower value of testosterone at later times after surgery was a better predictor of complications. CONCLUSION:Patients with low testosterone level were prone to higher postoperative complications, which was evident in both sexes. However, further studies are necessary to support this result.