BACKGROUND The objective of this paper was to assess the complications following sentinel lymph node biopsy (SLNB) in breast cancer patients using the SentiMag® method. MATERIAL AND METHODS The study material consisted of 368 patients who had received the SLNB procedure in combination with wide local excision (WLE), simple mastectomy or who had an autonomous SLNB procedure in the period from January 2014 to September 2017. The final study group consisted of 303 patients who attended follow-up consultations. RESULTS Sensory disturbances in the arm occurred in 12 patients (9.9%), including 3 patients (1.5%) after WLE and 9 patients (8.4%) after simple mastectomy. Restricted mobility in the upper limb was experienced by 9 patients (7.1%), including 3 patients (1.5%) after WLE and 6 patients (5.6%) after simple mastectomy. Minimal-degree lymphedema developed in 9 patients (7.5%), including 2 patients (1%) after WLE and 7 patients (6.5%) after simple mastectomy. A significant correlation was demonstrated between the incidence of these complications and the number of lymph nodes dissected. A significantly higher incidence of paresthesia and lymphedema was revealed for simple mastectomy with SLNB when compared to WLE with SLNB. Discolorations upon tracer administration were observed in 47 patients (15.5%). CONCLUSIONS SentiMag® is a safe sentinel lymph node identification method used in breast cancer and has a low risk of complications. The rate of complications increases together with the number of dissected lymph nodes and the extent of the surgery. The possibility of temporary discolorations on the skin should be communicated to the patients explicitly prior to surgery.