The ethmoid and maxillary sinuses are present at birth. They can be detected radiographically at 5–6 months of age. The ethmoid sinuses grow rapidly in the first few years of life. Their growth slows significantly by 7 years of age. They reach full size by 12–14 years of age. The maxillary sinuses also grow rapidly in the first few years of life mainly during the third and fourth years of life. After 7 years of age, growth accelerates inferiorly after the permanent teeth have erupted. They reach full growth by 15 years of age. The frontal and sphenoid sinuses start aerating by 4 years of age. Their development starts accelerating by 8 years of age and full development is reached by 18 years of age. Because of this development, the main sinuses involved in children with chronic rhinosinusitis (CRS) are the ethmoid and maxillary sinuses [17].