Kawasaki disease is a vasculitis affecting medium-sized vessels. It occurs predominantly in childhood and is often difficult to diagnose, as clinical manifestations appear gradually and in varying combinations. Biochemical diagnostic tools are limited, making early recognition crucial for timely treatment and for preventing serious complications such as coronary artery aneurysms or severe myocarditis. In this article, we present the case of a 14-month-old girl in whom the diagnosis was established only after a prolonged course. Her symptoms gradually evolved into the full clinical picture. During this period, she also had a concomitant Epstein-Barr virus infection, confirmed serologically. This case highlights the importance of continued investigation when the clinical presentation is incomplete.  Kulcsszavak: Kawasaki disease, vasculitis, aneurysm, Epstein-Barr vírus