We retrospectively analyzed the likelihood of regional nodal failure (RNF) for 1,624 patients with stage I or II invasive breast carcinoma treated with conservative surgery and radiotherapy (RT) at the Joint Center for Radiation Therapy (JCRT) between 1968 and 1985. The median follow-up time was 77 months. RNF was the first site of failure for 38 of the 1,624 patients (2.3%). The incidence of axillary failure for patients undergoing axillary dissection (AXD) who were irradiated to the breast only was 2.1% (nine of 420) for patients with negative nodes and 2.1% (one of 47) for patients with one to three positive nodes. The incidence of supraclavicular failure in these two groups was 1.9% (eight of 420) and 0% (zero of 47), respectively. The incidences of axillary and supraclavicular failure in patients without clinically suspicious axillary involvement who did not have AXD but were treated with RT were 0.8% (three of 355) and 0.3% (one of 364), respectively. Despite various combinations of salvage surgery, RT, and systemic therapy, only 47% of patients (18 of 38) achieved complete regional control after nodal relapse. We conclude that RNF is uncommon in patients treated to the breast alone following an adequate AXD when the axillary nodes are negative or when one to three nodes are positive. RNF is also uncommon in patients with a clinically uninvolved axilla treated with nodal RT without AXD. Symptoms of RNF can be controlled in most but not all patients. Further study is needed to determine if the benefits of RT in preventing a small number of symptomatic RNF outweigh the potential toxicity for any subgroup of patients.