Aim: Transanal endoscopic microsurgery (TEM) is used for the resection of large rectal adenomas and well or moderately differentiated T1 carcinomas. Due to difficulty in preoperative staging, final pathology may reveal a carcinoma not suitable for TEM. Although completion total mesorectal excision is considered standard of care in T2 or more invasive carcinomas, this completion surgery is not always performed. The purpose of this article is to evaluate the outcome of patients after TEM-only, when completion surgery would be indicated. Methods: In this retrospective multicenter, observational cohort study, outcome after TEM-only (n = 41) and completion surgery (n = 40) following TEM for a pT2–3 rectal adenocarcinoma was compared. Results: Median follow-up was 29 months for the TEM-only group and 31 months for the completion surgery group. Local recurrence rate was 35 and 11% for the TEM-only and completion surgery groups respectively. Distant metastasis occurred in 16% of the patients in both groups. The 3-year overall survival was 63% in the TEM-only group and 91% in the completion surgery group respectively. Three-year disease-specific survival was 91 versus 93% respectively. Conclusions: Although local recurrence after TEM-only for pT2–3 rectal cancer is worse compared to the recurrence that occurs after completion surgery, disease-specific survival is comparable between both groups. The lower unadjusted overall survival in the TEM-only group indicates that TEM-only may be a valid alternative in older and frail patients, especially when high morbidity of completion surgery is taken into consideration. Nevertheless, completion surgery should always be advised when curation is intended.