PURPOSE : We tried to define the complications related to the degree of injury and the treatment modalities in surgically treated lateral condylar fracture of the humerus in children. MATERIAL : We experienced 42 children under 15 years of age who were diagnosed lateral humeral condylar fracture and treated by operation. The follow up periods were from 6 months to 39 months, average 15.2 months. There were 4 cases of Milch type I fracture and 38 cases of Milch type II fractures. According to the displacement, there were 9 cases of stage I fracture, 20 cases of stage II fracture, and 13 cases of stage III fracture. The age distribution was from 1.5yrs. to 13yrs.(average ; 5.2years) and there were 26 male children and 16 female children. METHOD : 6 cases of stage I fracture and 2 cases of stage II fracture were treated by maunal reduction and percutaneous K-wire fixation. 3 cases of stage I fracture revealed incongruency of articular surface, 18 cases of stage II fractures and 13 cases of all stage III fracture were treated by open reduction and percutaneous K-wire fixation. RESULT : There 13 cases of lateral bony hypertrophic(30.9%), 4 cases of minimal limitation of elbow joint motion(9.5%), 3 cases of hypertrophic skin scar(7.1%), 2cases of pin tract infection(4.8%), one case of slight decrease of carrying angle(2.4%). Howerer there was no serious complication such as nonunio or cubitus valgus. Limitation of elbow joint motion occurred significantly higher in Milch type I fracture(2 cases, 50%) than Milch type II fracture(2 cases, 5.3%)(p<0.05). Lateral bony hypertroph occurred significantly higher in open reduction(12cases, 35.3%) than in manual reduction(one case, 12.5%)(p<0.05). Also lateral bony hypertrophy occurred higher in moderate and severe displaced fractures(stage II and III ; 12cases, 36.4%) than in minimal displaced fractures(stage I ; one cases, 11.1%)(p<0.05). CONCLUSION : In the displaced lateral humeral condylar fractures in children, the serious complications can be avoided through selecting adequate treatment modality. In the case of open reduction, the possibility, the possibility of lateral bony hypertrophy should be minded.