In the last 15 years, sentinel lymph node biopsy (SLNB) for patients with malignant melanoma (MM) has been introduced into the clinical practice. Our aim was to make a retrospective analysis of clinical results in order to assess the success ratio of SLNB and the variables affecting it in MM patients, treated in the Oncology Center at the University Hospital “Dr George Stranski” - Pleven, Bulgaria for a 4-year period. A research index card was used to process the oncologic files of 82 out of 102 patients with MM, treated and monitored at the Oncology centre between 01.01.2008 and 31.12.2011. TNM-stages, Breslow and Clark levels, location, characteristics of the skin lesion, diagnostic excision, type of lymph node dissection, number of SLN, localization of SLN, etc. were registered in the index card. SLNB staging was carried out in 28 patients. Sentinel lymph nodes were found in 22 of them. The success ratio of the method was 78.6%. Histologically, metastatic SLN were found in 4 cases. The Patent Blue Dye method was used in 22 of the cases (78%). A combined radiocolloid and dye method was used in 5 cases (18%). A radiocolloid method was used in 1 case (4%) only. Our research showed that more therapeutic lymph node dissections were performed in cases of locally advanced MM, which in turn worsened the clinical results. According to our research, the SLNB success ratio depends on the precision of diagnostic excision (p=0.019), lesion location (p=0.015), Clark level (p=0.0229), mapping method (p=0.08) and the type of melanoma (p=0.088).