We investigated prevalence of coincident infections in acute Kawasaki disease (KD) to know the possible effects of infections on diagnosis of KD, clinical course, therapy decision and coronary outcomes. Single center consecutive 344 KD patients hospitalized in our institution, between January 2009 and December 2013 were retrospectively analyzed. Patients those were positive for bacterial culture, rapid antigen tests or elevated levels of pathogen specific antibodies were counted as KD patients with infection. Pathogen unproven patients those presented with apparent respiratory or gastrointestinal symptoms regarding infections were also counted as KD patients not to underestimate number of patients with suspected infections. Overall, 125 KD patients were grouped as KD patients with infection (Group1). Group1 included 125 patients with 73 upper respiratory tract infection, 21 bronchitis, 7 pneumonia, 3 acute otitis media and 21 gastroenterocolitis, respectively. Remaining 219 KD patients were grouped as KD without infection (Group2). Appropriate antibiotic or antiviral treatments were done for each pathogen proven infection. Distribution of age and sex, day of admission, diagnosis and treatment, prevalence of initial treatment regimen and rate of additional therapy, duration of fever, laboratory findings except serum albumin value, and coronary outcomes were similar between the groups. We showed that presence of coincident infections have no effects on clinical course, treatment decision and coronary outcomes on KD.