Diagnostic imaging of Paget's disease of bone should provide more than a diagnosis. It should aim at assessing the distribution of the lesions, their degree of activity, their potential complications and their response to therapy. This goal can be reached by using simple methods (bone scintigraphy and conventional radiography), as long as one keeps in mind both the natural evolution of the disease and the changes it may show in case of superadded factors such as fissure-fractures, immobilization, and osteopenia. In clinical practice, bone scintigraphy is particularly apt to assess the distribution of the lesions, as well as their extent and degree of activity. Conventional radiography remains the best tool for establishing the diagnosis and the differential diagnosis of Paget's disease of bone, as well as for detecting its common complications, such as fissure fractures, diaphyseal bowing or superadded arthropathy. Additional methods such as CT should only be used when specific complications (such as spinal stenosis or superadded tumor) are suspected. In patients under antiosteoclastic therapy, careful sequential X-rays of one or two selected pagetic areas initially showing focal bone resorption represent a unique modality for monitoring focal treatment efficacy. Such therapy may indeed improve the biological parameters of the disease without correcting the negative bone balance within the most active lesions.