Paranasal sinus anatomy and variations have gained interest with the introduction of functional endoscopic sinus surgery and the concept of the ostiomeatal complex. Anatomical variations can be divided in structural abnormalities, (increased) pneumatization and supplementary openings. Most anatomical variations are equally found in control and sinusitis patients. The anatomical variations which are most commonly associated with sinus pathology are septal deviations, true conchae bullosae and supplementary maxillary ostia but the latter one only when recycling is present. The knowledge of anatomical variations is most important in the surgical management and specifically in the prevention of complications.