Objective: A restrospective analysis of the clinical picture (inflammatory markers, characteristics of fever, comorbidities) in different clinical manifestations of human adenovirus (HAdV) infections confirmed using point-of-care testing in a group of hospitalized children. Material and Methods: A total of 135 children with confirmed HAdV infections were divided into three groups according to their clinical symptoms: Group A—respiratory (n = 57), Group B—gastrointestinal (n = 40), and Griup C—mixed (n = 38). Results: Respiratory and mixed HAdV-infected patients, as compared with gastrointestinal HAdV-infected patients, were younger (median value (Me) and interquartile range (IQR) (months): 17 (12–30) and 17 (12–27) vs. 30 (16–50), p = 0.04), had a longer duration of fever (days): 3 (1–5) and 3 (1–4) vs. 1 (1–2), p = 0.01), and had higher C-reactive protein values (mg/L): 29.2 (10.4–69.1) and 28.7 (10.8–49.1) vs. <5 (<5–20.6), p < 0.001). There were no correlations between CRP levels and patient’s age, fever duration, the occurrence of acute otitis media and lower respiratory tract infection, and antibiotic treatment before admission. Conclusions: Patients with respiratory HAdV infections have fevers more often, the duration of the fever prior to admission is longer, and CRP levels are higher.