The diagnosis of acute pyelonephritis in adults is predominantly made by a combination of typical clinical features of flank pain, high temperature and dysuria combined with urinalysis findings of bacteruria and pyuria. Imaging is generally reserved for patients who have atypical presenting features or in those who fail to respond to conventional therapy. In addition, early imaging may be useful in diabetics or immunocompromised patients. In such patients, imaging may not only aid in making the diagnosis of acute pyelonephritis, but more importantly, it may help identify complications such as abscess formation. In this pictorial review, we discuss the role of modern imaging in acute pyelonephritis and its complications. We discuss the growing role of cross-sectional imaging with computed tomography (CT) and novel magnetic resonance imaging (MRI) techniques that may be used to demonstrate both typical as well as unusual manifestations of acute pyelonephritis and its complications. In addition, conditions such as emphysematous and fungal pyelonephritis are discussed.