We reviewed retrospectively 53 cases of supracondylar fracture of humerus in children which were severely displaced(Gartland type III). All patients were treated with closed reduction and percutaneous pinning. Purpose of this study is to evaluate the residual effect of incompletely reduced fragment, especially of rotation of distal fragment(represented by fish-tail sign) on clinical relults. The quality of reduction was determined by carrying angle, varus tilting, existence of fish-tail sign and medial displacement. Of the 53 elbows, fish tail signs only presented in twelve cases(50.0%), medial tilting combined with fish tail in five(20.8%) and medial displacements in seven cases(29.2%). Final results by Flynn et al. were as follows; Excellent was in 40 cases(15.9%), Good in 6(11.3%), Fair in 1(1.8%), poor in 6(11.3%). Six cases of poor outcomes resulted from cubitus varus deformed elbow, of which cubitus varus deformity developed in 5 cases of medial tilted distal fragment, one developed in medially displaced fragment, and cases presented with fish tail sign(rotation of distal fragment) had no contribution to cubitus varus deformity yielding acceptable clinical results. In conclusion, even though the quantification of fish tail sign is needed, fish tail sign only presenting on fluorscopy might be acceptable in operative room.