We present the case of an 8-year-old patient with a juvenile ossifying fibroma in the right mandibular angle and a radicular cyst in the left mandibular angle, which produced a major swelling at the level of the mandibular angles and prevented the correct eruption of the lower first molars. After the clinical and radiological (panoramic X-ray and dental scan of the mandible), the corresponding surgical treatment (cystectomy and remodelling) and histopathological study were carried out. Although juvenile ossifying fibroma is an uncommon clinical entity, its aggressive local behaviour and high recurrence rate mean that it is important to make an early diagnosis, apply the appropriate treatment and, especially, follow the patient up over the long term.