Introduction: Influenza is a relatively severe acute respiratory disease caused by influenza viruses. It causes numerous complications which may have a mortal outcome or require hospitalization. Aims: To show the clinical and laboratory characteristics of seasonal influenza in patients treated at the University Hospital for Infectious Diseases "Dr. Fran Mihaljević" in Zagreb in the season 2016/2017. Structure of the study: A retrospective study Subjects and Methods: The study involved population in adults (≥18 years of age) with a laboratory confirmed influenza diagnosis, treated at the University Hospital for Infectious Diseases "Dr. Fran Mihaljević" in Zagreb, in the period from December, 2016 to March, 2017. Patients without hematological laboratory analysis have been excluded from the study. Results: Statistical data processing has determined the frequency of individual influenza subtypes and the presence of chronic illnesses or conditions that may pose a risk of complications. A comparison was made between the clinical symptoms of seasonal influenza of the examined patients and the laboratory examination results according to age, gender, day and type of influence. Conclusion: By analyzing the clinical and laboratory characteristics of influenza of the patients in Croatia in the 2016/2017 season, the most prevalent type of virus was A/H3N2/ (84.5 %), with a mean age of 58.5 years. Virus H1N1/pdm09 was isolated in 10.7 % of patients and proved more frequent in patients without a chronic disease while H3N2 was more common in patients with a chronic disease. Lymphopenia is present in patients with H1N1/pdm09 and H3N2 viruses, monocytosis occurs on average in all influenza subtypes and transaminases are moderately elevated.