Background The Developmental Hip dislocation (DDH) has a high prevalence in our country and causes a huge morbility to our patient; furthermore, we need to find secure and efective methods to get a concentric hip reduction without complications rate increasing. In consecuence, there are a variety of methods to obtain the hip reduction; the medial approach has de advantage to spare the anterior approach used in pelvic osteotomies and for cosmetic point of view it uses a small wound incision at the groin level. Methods Pacients with less than 18 months old of age and 18 months mínimum follow-up with medial reduction for developmental hip dislocation were incluided. The procedures were performed at Roosevelt Pediatric Orthopaedic Institute IOIR or Jorge Piñeros Corpas Clinic-Saludcoop E.P.S by one of the tutors, GH or DO, between January of 2006 and June of 2011. The Salter and Kalamchi criteria for Avascular Necrosis (AVN) were reviewed in all the patients and interobserver concordance of tree Pediatric Orthopaedic Surgeons blinded for research purpose, also. Results 16 patients with 20 hips were incluided. We found AVN in 40% of patients but 75% of this porcent were graded I of Kalamchi stage. The interobserver concordance of AVN and Kalamchi stagement was higher than 0.6 of Kappa index. Discussion The medial open reduction of developmental hip dislocation in patients younger than 18 months old is a safe method; our AVN rate is similar to previus world reports about this technique, however when it occurs is mild due the vast majority was steged Kalamchi I (75%). The interobserver concordance for AVN assesment in X rays in experienced physicians is very accurate with a Kappa index of 0.6. Keywords: Developmental Hip Dislocation, medial approach, Avascular Necrosis, interobserver concordance.