Background: The histological features of osteitis in chronic rhinosinusitis (CRS) in animal studies induced by bacterial inoculation into maxillary sinuses revealed inflammatory involvement of the underlying bone matrix and/or the Haversian system; however, human studies do not mention these findings. The objective of this study was to investigate the inflammatory characterization of osteitis in CRS. Method: A prospective study of primary CRS patients undergoing sinus surgery was conducted (August 2012 to April 2013). Bone-mucosa samples were taken from a predetermined site that correlated to a computed tomography location. Radiological bone thickness was measured. A blinded histopathological assessment included inflammatory infiltrate of bone, periosteal reaction, presence of osteoblasts or osteoclasts, fibrosis, and the percentage of new woven bone to total bone thickness, together with an overall opinion of whether neo-osteogenesis was present. Results: Twenty-two primary CRS patients (age 45.8 ± 15.6 years; 59.1% female) were recruited. CRS with polyps accounted for 59.1% of patients. The bony thickness measured radiologically was a median 1.72 (interquartile range [IQR], 2.38; range, 0.3-12.14) mm. No samples (0%) had evidence of inflammatory infiltrate of bone; 90.9% had both osteoblasts present and new woven bone formation. Woven bone was greater with periosteal reaction (80.83% ± 9.25% vs. 47.50% ± 29.37%; p = 0.006), greater with osteoclasts present (80.00% ± 12.58% vs 59.00% ± 28.52%; p = 0.03), and greater when fibrosis was present (69.75% ± 24.14% vs 25.00% ± 7.07%; p = 0.003). Conclusion: Most primary CRS patients demonstrated evidence of new woven bone formation. True "osteitis" with inflammatory infiltrate of the bone was not observed. "Osteitis" is likely a process of neo-osteogenesis and bone remodeling, rather than bone inflammation in primary CRS.