Background Seasonal influenza causes substantial numbers of hospitalizations annually, and there is a need to identify prognostic markers of clinical outcomes in hospitalized influenza patients. Methods Patients hospitalized with influenza were included during four influenza seasons (2014-2018). On admission, patients were assessed by the CRB65, CRB, SIRS and qSOFA risk scores. “Severe outcome” was defined as treatment in intensive care unit and/or all of the following three clinical parameters: pneumonia, O2 supplementation and hospital stay ≥ 5days. Regression analyses were used to study effects of scores, influenza (sub)types and age on outcomes and treatment. Results A total of 156 patients with median age of 70 years were included. Patients with influenza A(H3N2) were older than those with B and A(H1N1). Older age was associated with fewer symptoms. Severe outcome was observed in 22% of the cases. High CRB, CRB65, SIRS and qSOFA scores at admission was observed in 60%, 46%, 40% and 29% of patients with severe outcome, respectively. Influenza (sub)types were not associated with severe outcome. Antiviral treatment was given to 37% of the patients, while 78% received antibiotics. The use of antiviral treatment increased during the study period. Patients with influenza B received less antiviral treatment. Conclusion This is the first study describing adult patients hospitalized with seasonal influenza in Norway. Risk scores, and particularly CRB, may be useful to predict severe outcome in influenza disease. More patients might have profited from antiviral therapy; including patients with influenza B infection.