Objectives Acute rhinosinusitis (ARS) has a high incidence. Diagnosis is clinical, and evolution is mostly self-limited. The aim of this study was to describe the sociodemographic characteristics and use of diagnostic tools and medications in patients with ARS. Design This is a prospective observational study in real-life clinical practice. Setting Patients with clinical diagnosis of ARS (n=2610) were included from ear, nose and throat clinics in Spain. A second visit at resolution was done. Participants Patients were classified according to the duration of symptoms: viral ARS (≤10 days), postviral ARS (>10 days, ≤12 weeks) and chronic rhinosinusitis (>12 weeks). Main outcome measures Sociodemographic characteristics, symptoms, disease severity, quality of life (Sino-Nasal Outcome Test-16), used diagnostic tools and medications, and the management performed by primary care physicians (PCPs) and by otorhinolaryngologists (ORLs) were assessed. Results Of the patients 36% were classified as having viral ARS, 63% postviral ARS and 1% as chronic rhinosinusitis. Working in a poorly air-conditioned environment was a risk factor (OR: 2.26, 95% CI 1.27 to 4.04) in developing postviral ARS. A higher number of diagnostic tools (rhinoscopy/endoscopy: 80% vs 70%; plain X-ray: 70% vs 55%; CT scan: 22% vs 12%; P<0.0001) were performed in postviral than viral cases. PCPs performed more X-rays than ORLs (P<0.0001). Patients, more those with postviral than viral ARS, received a high number of medications (oral antibiotics: 76% vs 62%; intranasal corticosteroids: 54% vs 38%; antihistamines: 46% vs 31%; mucolytic: 48% vs 60%; P<0.0001). PCPs prescribed more antibiotics, antihistamines and mucolytics than ORLs (P<0.0068). More patients with postviral than viral ARS reported symptoms of potential complications (1.5% vs 0.4%; P=0.0603). Independently of prescribed medications, quality of life was more affected in patients with postviral (38.7±14.2 vs 36.0±15.3; P=0.0031) than those with viral ARS. ARS resolution was obtained after 6.04 (viral) and 16.55 (postviral) days, with intranasal corticosteroids being associated with longer (OR: 1.07, 95% 1.02 to 1.12) and phytotherapy with shorter (OR: 0.95, 95% CI 0.91 to 1.00) duration. Conclusions There is a significant overuse of diagnostic tools and prescribed medications, predominantly oral antibiotics, by PCPs and ORLs, for viral and postviral ARS.