This case reports on the treatment of a radicular cyst in a child. The patient presented a periapical radiolucent area associated to a root from the maxillary left primary second molar. After the extraction of the root, marsupilization of the lesion was done and a fixed resin tube was placed in the alveolar hole. After twenty-five months the lesion was healing. This technique has proved to be effective and conservative for the treatment of radicular cysts in primary teeth.