Purpose: To evaluate the effect of pelvic radiotherapy (RT) in patients with stage IV rectal cancer treated with resection of primary tumor with or without metastasectomy. Materials and Methods: Medical records of 112 patients with stage IV rectal cancer treated with resection of primary tumor between 1990 and 2011 were retrospectively reviewed. Fifty-nine patients received synchronous or staged metastasectomy whereas fifty-three patients did not. Twenty-six patients received pelvic radiotherapy. Results: Median overall survival (OS), locoregional recurrence-free survival (LRFS), and progression-free survival (PFS) of all patients was 27, 70, and 11 months, respectively. Pathologic T (pT), N (pN) classification and complete metastasectomy were statistically significant factors in OS (p = 0.040, 0.020, and 0.002, respectively). RT did not improve OS or LRFS. There were no significant factors in LRFS. pT and pN classification were also significant prognostic factors in PFS (p = 0.010 and p = 0.033, respectively). In the subgroup analysis, RT improved LRFS in patients with pT4 disease (p = 0.026). The locoregional failure rate of the RT group and the non-RT group were 23.1% and 33.7%, showing no difference in the failure pattern of both groups (p = 0.260). Conclusion: Postoperative pelvic RT did not improve LRFS of all metastatic rectal cancer patients; however, it can be recommended to patients with pT4 disease. A complete resection of metastatic masses should be performed if possible.