We investigated how the diameter of coronary artery aneurysm (CAA) relates to the distribution immediately after Kawasaki disease (KD). Two hundred and four pts (155 males and 49 females) who had undergone selective coronary angiography (CAGs) less than 100 days after the onset of KD were studied. We measured the maximum diameter of each artery segment in the initial CAGs. We analyzed the relationship between the maximum diameters and the distribution of CAA. We divided the patients into four groups based on the maximum CAA diameter in each patient (large(L) ≥8 mm, medium(M) ≥6 and <8 mm, small(S) ≥4 and <6 mm, very small(VS) <4 mm) and counted the affected segments. There were 87, 61, 36, and 20 patients in groups L, M, S, VS, respectively. The number of segments with CAA in each group was L 6 ± 2, M 4 ± 2, S 2 ± 2, VS 2 ± 1. The number of affected segments in L was significantly more than M, and a large value for L indicated that involvement was significantly more likely to be bilateral. The larger the maximum diameter of CAA, the more extensive disease involvement and the more likely to be bilateral. A large maximum CAA can also indicate coronary involvement in the longitudinal directions. It is an important charcteristic in distribution of CAA caused by KD vasculitis.