The authors describe serial positron emission tomography (PET) and magnetic resonance imaging (MRI) studies in a patient with pathologically confirmed Rasmussen Encephalitis (RE). Results of initial PET and MRI studies were normal. Subsequent studies showed involvement of the percentral and postcentral gyri and the putamen on PET, and the precentral and postcentral gyri on MRI. Coregistration of PET and MR images showed good correlation between the precentral and postcentral gyri involvement. However, subcortical involvement occurred earlier on PET than on MRI. The authors demonstrate the evolution of changes on PET and MR images in a patient with RE. Despite early pathologic confirmation of RE, there were no definite structural or functional imaging changes on PET or MRI until 3 years after symptom onset. These findings demonstrate the variability of imaging changes in RE, and the need to carefully correlate electro-physiologic and clinical findings to confirm the diagnosis of RE.