Part I discusses the correlation between the clinical, radiology and histologic features with the three phases (incipient, mid- and late phase) of Paget's disease. In this section, we will discuss in detail the radiologic features by location as well as aberrant radiographic presentations in addition to secondary tumors such as post radiation sarcomas and giant cells tumors which occur in Paget bone. Because Paget's disease generally affects people in their middle and late ages, the differential diagnosis often includes metastatic disease and the differentiation can often be quite challenging. Moreover, metastatic disease to bones afflicted with Paget's disease can further add diagnostic confusion. These critical aspects will be discussed in this section of Paget's disease of bone.