OBJECTIVES: The aim of this study is to examine the differences between laboratory indicators at the first examination and follow-up examination of patients with adenovirus infection, to determine clinical and epidemiological characteristics of patients with adenovirus infection, and to examine whether there is a connection between patients' age and the development of complications and severity of clinical presentation. STUDY DESIGN: A historic cohort study. PARTICIPANTS AND METHODS: Based on the inclusion criterion (microbiologically confirmed adenovirus infection), the study included all patients with adenovirus infection (63 of them) examined and monitored at the Clinic for Infectology of Clinical Hospital Center Osijek in the period from October 2022 to October 2023. Demographic, epidemiological, clinical and laboratory dana were collected and analyzed from the patients' medical histories. RESULTS: Adenoviral infection was most commonly identified in patients under 18 years of age. Comorbidities were present in 23.8 % of patients, most frequently atopy. All patients developed fever, and common symptoms included cough (60.3 %), sore throat (55.6 %), and increased nasal secretion (47.6 %). Symptoms did not significantly differ with respect to the age of the patients. The most common clinical findings were tonsillitis (77.8 %), pharyngitis (68.3 %), and cervical lymphadenopathy (46 %). At the initial examination, laboratory results showed leukocytosis, borderline neutrophilia, decreased lymphocytes, and elevated CRP. At the follow-up, leukocytes, segmented neutrophils, and CRP levels were decreasing, while lymphocytes were increasing (although still within referent values). All patients recovered. CONCLUSION: The study showed that epidemiological data, clinical presentation, and laboratory test results of examined patients are consistent with typical adenovirus infection.