To compare the outcomes of the available systems that predict the risk of non-sentinel lymph node (non-SLN) metastasis and to evaluate the variability within a group of SLN-positive breast cancer patients. Predicted probabilities and scores for non-SLN metastasis were calculated with nine predictive systems for 120 SLN-positive patients who underwent a completion axillary lymph node dissection. The number of patients was calculated that were considered low risk or had a probability of a parts per thousand currency sign10% by at least one of the systems. For each nomogram, a box plot was constructed. All patients with a predicted probability of a parts per thousand currency sign10% according to the Memorial Sloan-Kettering Cancer Center (MSKCC) nomogram were selected, and a comparison was made with the probabilities predicted by the other systems. Nearly two-thirds (64.2%, = 77) of patients with SLN-positive breast cancer were allocated to a low-risk or low-probability group by at least one of the predictive systems. No patients were uniformly classified as low risk by all nine prediction models. At the group level, a considerable variation in the distribution of the predicted probabilities was observed. At the individual level, calculation of the predicted probabilities for the selected patients who were considered low risk (a parts per thousand currency sign10%) according to the MSKCC nomogram, showed even larger variations, ranging from 4 to 94%. This study shows that there is an unacceptably high variability in individual predictions when the predictive systems that are currently available are used to predict non-SLN metastasis in patients with SLN-positive breast cancer.