Lumbar spondylolysis is a common cause of low back pain in adolescent athletes. The results of complementary examinations can be used to distinguish among several clinical entities, whose therapeutic management will differ. We present the case of a 13-year-old football player who consulted for low back pain. Initial radiographic study showed unilateral right L5 spondylolysis. Isotopic study showed bone remodeling in both L5 pars. Therefore, a diagnosis of active right L5 spondylolysis and incipient left spondylolysis was made. Conservative treatment was provided and follow-up allowed the natural history of the two distinct processes to be observed. Viewing the lesion as a long-term process, allowed us to treat the patient with appropriate periods of rest. Due to the early diagnosis and the rapid disappearance of symptoms, the use of a brace to correct lordosis was not required.