Background Florid cemento-osseous dysplasia is a dynamic dysplastic bone abnormality where normal bone is replaced with fibrous tissue and various patterns of nonmature bone. Over time, these changes can be appreciated on imaging with the appearance of an early radiolucent entity becoming a mixed radiopaque/radiolucent entity and finally a predominantly radiopaque entity with a radiolucent rim of variable width. Discussion/Conclusions We present a case of florid cemento-osseous dysplasia, which did not follow a typical pattern, with imaging spanning 15 years in a single patient. The patient, a 41-year-old female, first presented to our clinic in 2008. Previous images from 2002 demonstrated typical patterns of florid cemento-osseous dysplasia in the mandible; radiolucent foci; and mixed radiolucent/radiopaque foci with epicenters located inferior to the apices of the teeth. In 2006, the pattern then changed to a wholly radiolucent one, and we interpreted this as being a simple bone cyst developing within the mixed radiopaque/radiolucent focus in the left mandible. Later images in 2013 showed peripheral new bone deposition; an appearance that we interpreted as being consistent with healing. Similar changes in the foci in the right mandible were also seen between 2013 and 2016. The left mandible showed fluctuations between both bone resorption and deposition over the years of imaging. External root resorption of the mandibular teeth also occurred, and these eventually involved the apical one-third of the affected teeth—a process that is rare, but occasionally seen. This case illustrates the dynamic clinical behavior that can occur with florid cemento-osseous dysplasia. It is important to recognize the range of variations in the presentation of this dysplastic bone entity and to correlate imaging findings with a clinical history to avoid misdiagnosis and mismanagement. Monitoring in certain cases may be necessary to confirm an initial interpretation of florid cemento-osseous dysplasia. Florid cemento-osseous dysplasia is a dynamic dysplastic bone abnormality where normal bone is replaced with fibrous tissue and various patterns of nonmature bone. Over time, these changes can be appreciated on imaging with the appearance of an early radiolucent entity becoming a mixed radiopaque/radiolucent entity and finally a predominantly radiopaque entity with a radiolucent rim of variable width. We present a case of florid cemento-osseous dysplasia, which did not follow a typical pattern, with imaging spanning 15 years in a single patient. The patient, a 41-year-old female, first presented to our clinic in 2008. Previous images from 2002 demonstrated typical patterns of florid cemento-osseous dysplasia in the mandible; radiolucent foci; and mixed radiolucent/radiopaque foci with epicenters located inferior to the apices of the teeth. In 2006, the pattern then changed to a wholly radiolucent one, and we interpreted this as being a simple bone cyst developing within the mixed radiopaque/radiolucent focus in the left mandible. Later images in 2013 showed peripheral new bone deposition; an appearance that we interpreted as being consistent with healing. Similar changes in the foci in the right mandible were also seen between 2013 and 2016. The left mandible showed fluctuations between both bone resorption and deposition over the years of imaging. External root resorption of the mandibular teeth also occurred, and these eventually involved the apical one-third of the affected teeth—a process that is rare, but occasionally seen.