Hip Joint diseases, such as osteoporosis, osteonecrosis, osteolysis, and osteoarthritis, induce pain and loss of mobility to millions of people around the world [55]. Stress analysis is useful for identifying the effects of the abnormality on joint functions. Finite element analysis (FEA) is a very powerful technique to the stress analysis of non-homogeneous and nonlinear systems just like the biological systems. In this thesis two abnormalities were simulated using finite element analysis in Ansys 12.1 simulation environment. These are Osteoporosis and Osteonecrosis, these abnormalities have been selected carefully to help generalize the results to as much abnormalities as possible since osteoporosis cause loss of Bone Mineral Density (BMD), thus its effects is on bone physical and mechanical properties, while osteonecrosis cause loss of geometry, thus its effects is on articulating geometry and both diseases can cause joint dysfunctions. In this thesis stresses, strains, and equivalent stresses were estimated in the head of femur during static stance for normal healthy adult, aging, osteopenia, osteoporosis and osteonecrosis with different stages, for the osteoporosis in the results a curve for BMD vs. strain has been sketched showing an increase up to four times in strain for the osteoporosis case compared to the normal case, for the osteonecrosis the results showed an increase in both, the stresses and the equivalent stresses, with a disturbance in the usual distribution of stresses around the neck of femur. These results can help the orthopedics surgeons to develop clear impression for what actually happens to the joint from mechanical point of view during osteoporosis and osteonecrosis, and since the study clarified the reasons of failure for these abnormalities. The results can help the specialist to predict the joint failure before its actual occurrence.