In a method and an apparatus for automatically generating an optimal 2-dimensional (2D) medical image from a 3D medical image, at least one virtual plane crossing a 3D volume is generated from 3D volume image data for showing part of a patient's body in a 3D manner, at least one 2D image representing a cross section of the part of the patient's body is generated by applying the 3D volume image data to the virtual plane, and a 2D image suitable for diagnosis of the patient having a feature most similar to a target feature from among the at least one 2D image is output.