Sonographic examination of the knee has been proposed by several authors in the past as a simple and reliable method to diagnose Osgood-Schlatter disease (OSD). Ultrasound was used to compare the knees of 25 boys and 10 girls with typical OSD with 35 symptom-free knees of an aged-matched group of children. Based on recorded data, patients were categorized (one affected knee in each individual) according to the classification system proposed by De Flaviis et al. in 1989. The results included the following pathological findings: pretibial swelling, fragmentation of the ossification center, insertional thickening of the patellar tendon, and excessive fluid collection in the infrapatellar bursa. Of our patients, 26% fell into the type 1 category, 43% were type 2, 20% type 3, and 11% type 4. This distribution of cases was found to be statistically similar to the initial findings reported by De Flaviis and colleagues. This study therefore supports the validity and reproducibility of their classification method for the ultrasonographic evaluation of children with OSD. This is only the first step, and further assessment of this classification is still required to elucidate its clinical as well as its prognostic value.