OBJECTIVES: To provide insight into healthcare utilisation of rhinosinusitis, compare data with clinical practice guideline recommendations and assess practice variation. DESIGN: Anonymised data from claims reimbursement registries of healthcare insurers were analysed, from 1 January 2016 until 31 December 2016. SETTING: Secondary and tertiary care in the Netherlands. PARTICIPANTS: Patients ≥18 years with diagnostic code "sinusitis." MAIN OUTCOME MEASURES: Healthcare utilisation (prevalence, co-morbidity, diagnostic testing, surgery), costs, comparison with guideline recommendation, practice variation. RESULTS: We identified 56 825 patients, prevalence was 0.4%. Costs were € 45 979 554-that is 0.2% of total hospital-related care costs (€21 831.3 × 10 6 ). Most patients were <75 years, with a slight female preponderance. 29% had comorbidities (usually COPD/asthma). 9% underwent skin prick testing, 61% nasal endoscopy, 2% X-ray and 51% CT. Surgery rate was 16%, mostly in daycare. Nearly, all surgical procedures were performed endonasally and concerned the maxillary and/or ethmoid sinus. Seven recommendations (25%) could be (partially) compared to the distribution of claims data. Except for endoscopy, healthcare utilisation patterns were in line with guideline recommendations. We compared results for three geographical regions and found generally corresponding rates of diagnostic testing and surgery. CONCLUSION: Prevalence was lower than reported previously. Within the boundaries of guideline recommendations, we encountered acceptable variation in healthcare utilisation in Dutch hospitals. Health reimbursement claims data can provide insight into healthcare utilisation, but they do not allow evaluation of the quality and outcomes of care, and therefore, results should be interpreted with caution.