The imaging features of chronic periaortitis resemble those of infected aneurysms. Two illustrative cases of chronic periaortitis, in which the etiologies were caused by IgG4-related disease, are presented. The first case involved a 68-year-old man who presented with vague discomfort in his lower abdomen. The second case was a 42-year-old man who presented with a fever of 38°C and persistent, vague chest discomfort. Both cases demonstrated an increased amount of connective tissue around the aorta in computed tomography images and low intensity in the T2-weighed sequence and high intensity in the diffusion-weighed sequence, suggesting the presence of inflammation, in the magnetic resonance imaging. Negative blood cultures, elevated IgG4 levels, and pathological findings confirmed the diagnosis as chronic periaortitis due to IgG4-related disease. This is a newly recognized syndrome of unknown etiology, characterized by a fibroinflammatory condition, tumefactive lesions, and a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells. Both cases were successfully treated with corticosteroids. Infected aneurysms need to be carefully differentiated from this syndrome in view of the similar imaging features.