The primary aim of this study was to characterise complications, identify predictors of postoperative morbidity and mortality and to evaluate existing risk prediction models in elderly rectal cancer patients. An observational single-centre study of 330 consecutive patients > 75 years treated in 1994-2006. Analyses were performed by age group: 75-79 years, 80-85 years and > 85 years. Total observed in-hospital morbidity was 48.7 %. In multivariate analysis, age (OR 1.04, 95 % CI 1.01-1.08, p = 0.04), ASA grade a parts per thousand yenaEuro parts per thousand 3 (p = 0.01), acute presentation (OR 1.67, 95 % CI 1.2-13.2, p = 0.02) and major surgery (APR OR 3.72, 95 % CI 1.37-10.15, p = 0.01, LAR OR 2.98, 95 % CI 1.14-7.79, p = 0.03, Hartmann OR 5.46, 95 % CI 1.60-19.28, p = 0.02) were independent risk factors for postoperative morbidity. The 30-day mortality was 6.3, 6.4 and 14.3 % (p = 0.146) in the three age groups, and the 100-day mortality was 8.7, 10.1 and 22.2 % (p = 0.03), respectively. ASA group 3 (OR 6.21, 95 % CI 4.39-27.69, p = 0.017), ASA group 4 (OR 32.6, 95 % CI 5.12-207.75, p < 0.001) and acute presentation (OR 6.48, 95 % CI 1.62-25.99, p = 0.008) increased the risk of 100-day mortality. The Physiological and Operative Severity Score for enUmeration of Mortality and Morbidity (POSSUM) observed/estimated (O/E) ratio for morbidity was 1.05. For 30-day mortality, the colorectal POSSUM (Cr-POSSUM) O/E ratio was 0.74, Surgical Risk Scale 0.61 and the Association of Coloproctology of Great Britain and Ireland (ACPGBI) mortality model 0.63, and for 100-day mortality, ratios were 1.12, 0.91 and 0.95, respectively. In this series, age increased the risk of in-hospital morbidity and 100-day mortality. Cr-POSSUM, SRS and ACPGBI overestimated 30-day mortality but predicted 100-day mortality with a high degree of accuracy. POSSUM correctly predicted in-hospital morbidity.