Aim: Dissection in the mesocolic plane is considered by some medical professionals to be crucial in complete mesocolic excision. We aimed to assess whether intramesocolic plane dissection is associated with a risk of recurrence after complete mesocolic excision for right-sided colon cancer. Method: This is a single-centre study based on prospectively registered data on patients undergoing resection for Union for International Cancer Control Stage I–III right-sided colon adenocarcinoma during the period 2010–2017. Patients were stratified in an intramesocolic plane group or a mesocolic plane group based on a prospective assessment of fresh specimens by a pathologist. Primary outcome was the 4.2 year risk of recurrence after inverse probability treatment weighting and competing risk analyses. Results: Of 383 patients, 4 (1%) were excluded as the specimen was assessed as muscularis propria plane, 347 (91.6%) specimens were deemed as mesocolic and 32 (8.4%) as intramesocolic. The 4.2 year cumulative incidence of recurrence after inverse probability treatment weighting was 9.1% (95% CI 6.0%–12.1%) in the mesocolic group compared with 14.0% (3.6%–24.5%) in the intramesocolic group with an absolute risk difference in favour of mesocolic plane dissection of 4.9% (−5.7 to 15.6, p = 0.37). No difference was observed in the risk of local recurrence, death before recurrence or overall survival after 4.2 years between the two groups. Conclusion: Mesocolic plane dissection can be achieved in more than 90% of patients. The classification seems to be a guide for good surgical practice and not to be used for research purposes.