Disclosed are an apparatus and a method for determining lesion similarity of a medical image. The apparatus for determining lesion similarity according to one aspect of the present invention may comprise: an image input unit for receiving a reference image comprising a reference lesion area, and a target image comprising a target lesion area; and a similarity determination unit for determining similarity of the reference lesion area and the target lesion area by applying an advantage weight, which increases as getting closer to the center of the reference lesion area, to pixels included in a first area of the reference lesion area, and a penalty weight, which increases as getting farther away from the reference lesion area, to pixels included in a second area of the target lesion area.