Objectives: Benign bone tumors localized around the knee are common incidental findings in children and young adults during radiographic evaluation. This study aimed to investigate the prevalence and features of incidental benign bone tumors on knee radiographs in children and young adults according to age. Materials and Methods: After a retrospective review of 296 patients who visited the orthopedic outpatient clinic of our faculty hospital without a sign of a bone tumor around the knee between January and April 2022, a total of 38 patients younger than 35 years of age were included. We evaluated the knee radiographs and examined the prevalence and type of incidental benign bone tumors, and radiological features. Results: The mean age of the 21 male and 17 female patients was 17.5 years (range, 7 years to 34 years). Thirty-eight benign bone tumors including 23 non-ossifying fibromas (NOF) or cortical fibrous defects (CFD), 9 osteochondromas, 3 enostoses, 2 fibrous dysplasia, and 1 enchondroma were identified. The prevalence of incidental benign bone tumors of the knee was 12.8%. The most common incidental benign bone tumor was NOF or CFD with a prevalence of 7.8% and was more frequent in the second decade of life, followed by osteochondroma (3%). Conclusion: This study defines the incidental benign bone tumors on knee radiographs in children and young adults and provides useful evidence and information from a perspective of an orthopedic doctor. We recommend considering these incidental benign bone tumors and their features around the knee if unfamiliar findings appear or when counseling patients and their familie