Background: Breast cancer is the most common female cancer and the second leading cause of cancer death among women. Seroma is a pocket of clear serous fluid that develops in the body after surgery. Seroma is thought to be caused by the fact that the mastectomy operation leaves a lot of an empty space which can ooze serous fluid causing it to gather up in the space beneath the wound. This study aimed to evaluate the mechanical closure effect of the dead space by suture fixation of the mastectomy flaps to the underlying chest wall on the seroma formation after mastectomy