The purpose of this study was to perform an overall evaluation and comparison of the success rate of modified radical mastectomy by harmonic scalpel and monopolar electrocauter. The prospective study included all of the patients that were planned for and mastectiomized because of breast carcinoma during July 1st 2008 until December 21 st 2008 at the Department of Surgery and Urology, University Hospital Mostar. Duration of the surgical procedure, intraoperative blood loss and operational drain secretion was measured and registered. Leukocyte number (Le), interleukin 6 (IL-6), C-reactive protein (CRP) and erythrocyte sedimentation rate was tested and registered out of peripheral venous blood before the operation, 4 hrs after it, as well as on the first, second and third day after the operation. Every patient was tested for postoperative pain intensity, amount of administered analgesics during hospital stay, number and types of postoperative complications; also the time needed for return to everyday activities was registered. 61 patients were included in the study. 31 patients were operated with the harmonic scalpel, and 30 of them with the monopolar electrocauter. There is no statistically significant difference between the operation time in the two groups: 78.50±17.50 minutes by harmonic scalpel and 82.50±18.50 minutes by electrocauter (p=0.796). The smaller amount of intraoperative blood loss is statistically significant in the group of patients mastectomized by harmonic scalpel 78±31 ml compared to 256±112 ml in the group mastectomized by electrocauter (p<0.001); as is the total operational drain secretion: patients mastectomized by harmonic scalpel 540±390 mL compared to 960±710 mL in patients mastectomized by electrocauter (p<0.001). There is no statistical difference in the number of leukocytes in blood after modified radical mastectomy using the harmonic scalpel or electrocauter (p=0.957), or in erythrocyte sedimentation rate (p=0.114), CRP (p=0.071) and IL-6 (p=0.082). The duration of postoperative hospital stay does not differ statistically between the two groups, nor does the postoperative pain intensity, amount of administered analgesics, number or types of postoperative complications, as well as the time needed for return to everyday activities. Therefore using the ultrasound harmonic scalpel in comparison to monopolar electrocauter brings certain advantages, which however do not contribute significantly to the total success rate of the operation