Prospective studies of complications due to acute rhinosinusitis are lacking, bacterial cultures are hard to obtain and the role of airborne allergies, viruses and immunoglobulin levels are unclear. The aim was to investigate the role of bacteria, viruses, allergy and immunoglobulins in children hospitalized due to rhinosinusitis. A prospective cohort study in Stockholm, Sweden, of children up to 18 years of age, hospitalized due to acute bacterial rhinosinusitis, from April 1st, 2017 to April 1st, 2020. Of 55 children included, 51% had a positive viral nasopharyngeal PCR and 29% had a positive allergy sensitization test. A higher percentage of middle meatus cultures were positive for bacterial growth compared to nasopharyngeal and displayed a wider array of bacteria. Dominating bacteria were S. milleri in surgical (7/12 cases), S. pyogenes in middle meatus (13/52 cases), and S. pyogenes and H. influenza in nasopharyngeal cultures (8/50 cases respectively). Nasal cultures were negative in 50% of surgical cases. An association was found between S. pyogenes and peak CRP; H. influenzae and peak CRP; S. pneumoniae and peak CRP; and possibly between M. catarrhalis and days of IV antibiotics. Further, an association between influenza A/B and S. pyogenes; a positive viral PCR and lower grade of complication and peak CRP; and a possible association between influenza virus and lower grade of complication. Allergy sensitization was possibly associated with a higher number of days with IV antibiotics. No immunoglobulin deficiencies were found. There seem to be differences in the patterns of bacterial growth in nasopharyngeal, middle meatus and surgical cultures in children with complications to acute bacterial rhinosinusitis. Presence of certain viruses and sensitization to airborne allergies seem to play a role in complications to acute bacterial rhinosinusitis in children.