BACKGROUND: Clinically, locoregional recurrences following mucinous tumor resection are often experienced. However, it remains unclear whether mucinous tumors directly affect local recurrence or not, and if so, the mechanism is not known. Therefore, we investigated whether mucinous tumors are associated with locoregional recurrence after pulmonary resection and whether mucus extension is a risk factor for locoregional recurrence. METHODS: The data of 152 patients who underwent pulmonary resection for metastases were reviewed. When mucus was partially or wholly present in the tumor based on macro- or microscopic identification, we assigned the tumor as mucinous. In mucinous tumors, when mucus was identified within the air spaces in the normal lung parenchyma, beyond the edge of the tumor, we assigned the tumor as positive for "mucus extension." RESULTS: The 5-year cumulative incidence of locoregional recurrence in patients with mucinous tumors was 48.1%, which was significantly higher than that observed in those with non-mucinous tumors (14.9%). Within the mucinous tumor, the presence of mucus extension beyond the tumor edge was an independent risk factor for locoregional recurrence after pulmonary resection (hazard ratio, 5.52; P = 0.019). CONCLUSIONS: During the resection of mucinous cancer, surgeons should maintain sufficient distance from the tumor edge to prevent locoregional recurrences.