Objective: To discuss how the results of internal mammary lymph node biopsy at the time of autologous fl ap reconstruction in both the immediate and delayed setting may impact breast cancer treatment and the aesthetic outcome of autologous mastectomy reconstruction. Background:The internal mammary vessels are primary recipient vessels for autologous breast reconstruction with deep inferior epigastric artery perforator fl aps. During exposure and preparation of recipient vessels, the internal mammary lymph nodes when discovered are submitted to pathology. We have found in some patients, these internal mammary lymph nodes return positive results in patients with clinically and histologically negative axillary nodes and negative preoperative MRI/PET scan imaging. We wished to examine if these results had an impact on the radiation or chemotherapy management of the patients post-operatively. We have also sought to provide long-term follow-up on patients who have been found to have positive internal mammary lymph nodes. Methods:We performed a retrospective review of patients with breast cancer who underwent autologous breast reconstruction with deep inferior epigastric artery perforator fl aps. A specifi c chart review was performed on all patients found to have a positive result at the time of internal mammary lymph node biopsy.Results: Between 2008 and 2020 a total of 18 patients with positive internal mammary lymph nodes were identifi ed after internal mammary recipient harvest and visible lymph node biopsy. In three cases the internal mammary lymph node was positive when the axilla was negative. In 3/18 (16%) cases the patient's stage was changed based on the incidental fi ndings of the internal mammary nodes. Positive results changed post-operative radiation management in all patients. In only 1/16 (6%) cases was there suspicion on preoperative MRI. There were no instances of pneumothorax or other serious complications associated with the internal mammary lymph node biopsy.Conclusions: Incidental internal mammary lymph node biopsy performed during microvascular autologous breast reconstruction may prove positive for metastatic spread despite negative pathology results of the axillary lymph nodes. This may be seen even in patients with a normal pre-op MRI. Internal mammary node biopsy is feasible without serious adverse events when performed at the time of recipient vessel dissection. If preoperative imaging or intraoperative direct examination of the internal mammary nodes raises suspicion, frozen section evaluation may change fl ap harvest selection to acquire more perforators and potentially alter fl ap inset to protect the autologous fl ap from the adverse effects of radiation.