peer reviewed ; Osteochondrosis (OC), a developmental orthopaedic disease, is consecutive to a defect in the endochondral ossification process, and can result in formation of an osteochondral fragment (osteochondrosis dissecans). Our objective is to establish the prevalence of osteochondrosis in Wallonia, and describe the main observed lesions. One hundred forty-two Warmblood horses, aged from 12 to 36 months, underwent a systematic X-ray examination. Sixty-three of these horses (44.4 %) presented one or more OC lesions, 46 (32.4 %) of them with an articular fragment. This prevalence is similar to those observed in Dutch Warmblood horses (44.3 %). The localisation of the lesions was as follows: 25 (17.6 %) of the experimental group showed one or more lesions in the hindlimbs fetlocks, 23 (16.2 %) in the hocks, 21 (14.8 %) in the stifles and 14 (9.9 %) in the forelimbs fetlocks. The medial ridge of the talus is the most frequently injured anatomical site in our study. This lesion was observed in 12 horses (8.4 %), a prevalence that is by far higher than those observed in Dutch Warmblood horses (2.9 %). Not any significant difference was observed between males and females. The high prevalence and the clinical and economic consequences of this disease in the horse’s industry fully justify further research in order to improve the understanding of its pathogenic process. ; Ann. Méd. Vét., 2008, 152 (3), pp 131-137 Prévalence de l’ostéochondrose chez le cheval de sport en Wallonie VANDER HEYDEN L., SERTEYN D., CAUDRON I., VERWILGHEN D., DELIEGE B., LEJEUNE J.-P. Résumé : L’ostéochondrose (OC) est une affection ostéo-articulaire juvénile, consécutive à une non-ossification de l’os endochondral et pouvant entraîner la présence de fragments ostéochondraux (ostéochondrose dissécante). L’objectif de notre étude est d’établir la prévalence de cette affection en région wallonne, et de décrire les principales lésions observées. Cent quarante-deux poulains de sport nés en Wallonie, âgés de 12 à 36 mois, ont été radiographiés. ...