Subsequent displacement of nondisplaced or minimally displaced fractures of the lateral humeral condyle while immobilized in plaster may contribute to severe complications. The possibility of assessing the stability of such fractures may be a help in planning the initial treatment. Our prospective investigation of 112 children aged 1-11 years aimed at describing radiographic criteria for prognosticating the stability of the fractures. According to the radiographic findings, the fractures were allocated to one of three groups representing stable fractures, fractures with undefinable risk, and fractures with high risk of later displacement. All children were treated with splinting only. Sixty-five fractures were classified as stable and turned out to be so without exception. Displacement occurred in six of 35 (17%) of the fractures judged uncertain and in five of 12 (42%) of those judged unstable. The subsequent displacement was 1 or 2 mm, and in one case, 3 mm. The defined criteria were found to be efficient in separating the stable and the high-risk fractures with acceptable confidence. The group of fractures with undecided risk of subsequent displacement was fairly large--one third of the total material. The implication the findings may bear to the treatment strategy of fractures is analyzed in a work in progress.