The management of internal mammary nodes (IMNs) in breast cancer is controversial. Surgical series from the 1950s showed that one third of breast cancer patients had IMN involvement, with a higher risk in patients with medial tumors and/or positive axillary nodes. IMN metastasis has similar prognostic importance as axillary nodal involvement. However, after three randomized trials showed no survival benefit from extended mastectomy compared with radical or modified radical mastectomy, IMN dissection was largely abandoned. Recently, lymphoscintigraphy studies have renewed interest in IMN evaluation. Approximately one fifth of internal mammary sentinel nodes are pathologic, although most centers do not perform IMN biopsies because of concerns about morbidity and lack of established survival benefit. In addition, results from randomized trials testing the value of postmastectomy irradiation and a meta-analysis of 78 randomized trials have provided high levels of evidence that local-regional tumor control is associated with long-term survival improvements. This benefit was limited to trials that used systemic therapy, which was not routinely administered in the earlier surgical studies, although the contribution from IMN treatment is unclear. IMN irradiation has also been shown to cause increased cardiac morbidity. Before mature results from current randomized trials assessing the benefit of IMN irradiation become available, lymphoscintigraphy may be used to help guide decisions regarding systemic and local-regional treatment. However, even in patients with visualized primary IMN drainage, the potential benefit of treatment should be balanced against the risk of added morbidity.