Abstract Purpose Predictive factors of non-sentinel lymph node (NSN) involvement at axillary lymph node dissection (ALND) have been studied in the case of sentinel node (SN) involvement, with validation of a nomogram. This nomogram is not accurate for SN micrometastasis. The purpose of our study was to determine a nomogram for predicting the likelihood of NSN involvement in breast cancer patients with a SN micrometastasis. Methods We collated 909 observations of SN micrometastases with additional ALND. Characteristics of the patients, tumours and SN were analysed. Results Involvement of SN was diagnosed 490 times (53.9%) with standard staining (HES) and 419 times solely on immunohistochemical analysis (IHC) (46.1%). NSN invasion was observed in 114 patients (12.5%), whereas 62.3% (71) had only one NSN involved and 37.7% (43) two or more NSN involved. In multivariate analysis, significant predictive factors were: tumour size (pT stage ≤10 mm or >11 and ≤20 or >20 mm odds ratio (OR) 2.1 and 3.43, micrometastases detected by HES or IHC OR 1.64, presence or absence of lymphovascular invasion (LVI) OR 1.76, tumour histological type mixed or not OR 2.64. The rate and probability of NSN involvement with the model are given for 24 groups, with a representation by a nomogram. Conclusion One group, corresponding to 10.1% of the patients, was associated with a risk of NSN involvement of less than 5%, and five groups, corresponding to 29.8% of the patients, were associated with a risk ≤10%. Omission of ALND could be proposed with minimal risk for a low probability of NSN involvement.