Computer-aided hip surgery planning and implant design applications require accurate segmentation of femoral head and proximal acetabulum.An accurate outer surface extraction of femoral head using marching cubes algorithm remains challenging due to deformed shapes and extremely narrow inter-bone regions.In this paper,we present an automatic and fast approach for segmentation of femoral head and proximal acetabulum which leads to accurate and compact representation of femoral head using marching cubes algorithm.At first,valley-emphasized images are constructed from original images so that valleys stand out in high relief.Otsu’s multiple thresholding technique is applied to seperate the images into bone and non-bone classes.Region growing method and threedimensional (3D) morphological operations are performed to fill holes in the bone.In the reclassification process,the bone regions are further segmented,and the boundaries of the bone regions are further refined based on Bayes decision rule.Finally,marching cubes algorithm is applied to reconstruct a 3D model and extract the outer surface of femoral head and proximal acetabulum.Experimental results show that this method is an accurate segmentation technique for femoral head and proximal acetabulum and it can be applied as a tool in medical practice.