Hydatid cysts may develop anywhere in the body as a result of the presence of a viable parasite (Echinococcus granulosus). Depending on the condition of the parasite, the host reaction, and therapy, the hydatid cyst will degenerate and may eventually collapse, leaving an area of calcification in the host tissue. The purpose of this pictorial essay is to demonstrate the use of MR imaging in the diagnosis of the various stages of hydatid disease and in monitoring response to therapy.