Acute bacterial sinusitis (ABS) is a common complication of a simple upper respiratory infection. Acute bacterial sinusitis and an upper respiratory infection, however, have different management plans. This article will help clinicians establish when a diagnosis of ABS can be made based on the latest guidelines from the American Academy of Pediatrics. Also covered will be the pathophysiology of ABS, the role of diagnostic imaging, the recognition of complications of ABS, and treatment options.