Axillary nodal involvement (ANI) remains an essential prognostic factor for breast cancer patients, as it implies the necessity of systemic adjuvant treatment and locoregional irradiation. Axillary dissection (AD) contributes to improved local disease control and may increase survival. However, AD results in a 10%-25% incidence of long-term side effects, particularly lymphedema. Moreover, many small primary lesions with low risk of ANI are now discovered by screening, and it is not clear whether AD should be used routinely in all such patients. Sentinel lymph node biopsy (SLNB) is a selective procedure that allows selective staging of the axilla with few side effects. However, indications for SLNB are not precisely defined yet, so some patients may be understaged and the axillary relapse rate may increase. This study was conducted to help clinicians assess the risk of ANI and analyzed six clinical and histological parameters to optimally recognize patients who might benefit from SLNB, with a minimal risk of false-negative rate. We retrospectively analyzed the ANI risk among 893 women treated by conservative surgery and radiation for T0, T1, or T2 invasive tumours < 3 cm in size. All patients underwent AD with sampling of a minimum of seven lymph nodes. In each case, we assessed the clinical and pathological tumor size, histological subtype (including grading), tumor location, age at diagnosis, and breast size. The global ANI rate in the entire cohort was 25.3%. In multivariate analysis, three variables were significantly predictive of the ANI risk: tumor size (P < 0.0001), histological subtype (P = 0.0005), and breast size (P = 0.004). By combining these parameters, we were able to define three categories of women with low (< 20%), intermediate (21%-25%), and high (> 25%) ANI risk. We suggest that women with nonpalpable (T0), T1 grade 1/2, and T2 < 3 cm tumors of medullary, mucinous, tubular, or papillary histological subtype are the best candidates for SLNB. For other patients with a higher ANI risk tumor, AD may still remain the best procedure to obtain accurate staging and definitive local control.