A method and apparatus for displaying a medical image of an object. A user input is received to select at least one position in a 2D medical image generated from volume data representing the object. A space region in the volume data is determined, which includes the selected position, where the space region is based on brightness of voxels included in the volume data. A 3D medical image is generated and displayed, representing the determined space region by performing volume rendering on the volume data. The space region may be a region of an organ, tissue, tumor, etc., of the overall object, which includes the position selected on the 2D image.