Background: Obesity is becoming a bigger health problem every year. Current research shows that the obesity-related metabolic problems are strongly associated with visceral fat and not subcutaneous fat. Visceral obesity (VO) is associated with a worse postoperative outcome in multiple fields of abdominal surgery. On the other hand, muscle mass is related to better postoperative outcome. In rectal cancer patients, we studied the influence of visceral obesity and muscle mass on postoperative complications. Methods: The visceral fat area (VFA) and skeletal muscle area (SMA) were determined on preoperative CT scans in 406 patients. The preoperative comorbidity, per-operative outcome and postoperative complications were extracted retrospectively from the patient files. VO was defined as a VFA > 100 cm 2 . Correlations between body composition, postoperative complications and LOS were studied. Results: In our study, 67% of the patients were classified as visceral obese. Mean body mass index (BMI) was higher in the VO group (26.6 ± 3.5 vs 23.5 ± 2.8; p < 0.001). Visceral obese patients had a higher prevalence of cardiac comorbidity (29% vs 13% p = 0.001), hypertension (36% vs 20% p = 0.002) and diabetes mellitus (16% vs 5% p = 0.002). In addition, VO patients had more operative blood loss (431 vs 310 mL; p = 0.008), longer operating time (166 vs 149 min p = 0.003) and more wound infections (14% vs 8% p = 0.048). Visceral obesity was associated with more complications (OR: 1.63 p = 0.043) and longer LOS (risk estimate: 1.18 p = 0.009). Conclusion: VO patients more often had a history of cardiac disease, hypertension and diabetes mellitus. Visceral obesity correlated with a worse outcome after surgery for rectal cancer.