Routine removal of the internal mammary chain (IMC) sentinel node in breast cancer patients remains a subject of discussion. The aim of this study was to determine the impact of routinely performed IMC sentinel node biopsy on the systemic and locoregional treatments plan. All patients with biopsy proven breast cancer who underwent a sentinel node procedure between 2002 and 2011 were included in a prospective database. In cases of IMC drainage, successful exploration of the IMC (i.e., sentinel node removed) and surgical complications were registered. If the removed sentinel node contained malignant cells we determined if this altered the treatment plan when practising the current guidelines. In total, 119 of the 493 included patients showed IMC drainage on lymphoscintigraphy. Exploration of the IMC was performed in 107 (89 %) patients; in 86/107 (80 %) exploration was successful. In 14/107 patients (13 %) the IMC sentinel node was tumor positive. Macro and micro metastases were found in eight and six patients, respectively. In the group of patients who underwent surgical exploration of the IMC, systemic treatment was changed in none, radiotherapy treatment in 13/107 patients (11 %). Routine sentinel node biopsy of the IMC does not alter the systemic treatment. Radiotherapy treatment is altered in a small proportion of the patients; however, solid scientific evidence for this adjustment is lacking.