A 58-month-old boy has complained of swelling on the left submandibular region for 3 months. Previous related dental treatment included pulpectomy and amalgam restoration of the left mandibular deciduous second molar. Clinical and radiographic examinations suggested the diagnosis of Garre's osteomyelitis of the left submandibular region. The possible etiology seemed to be severe caries of the mandibular second deciduous molar. In addition, a well-defined radiolucency with corticated border around the apex and interradicular areas of the right mandibular deciduous second molar was shown on the panoramic radiograph, which suggested an odontogenic cyst. After extraction of the left mandibular deciduous second molar, the swelling of the left submandibular region was decreased. Cyst enucleation was performed under general anesthesia and the excised specimen was sent for pathologic examination. A diagnosis of radicular cyst was confirmed microscopically. The right mandibular deciduous second molar and permanent tooth germ of the second premolar was also removed at the same time. There was no evidence of recurrence after 18 months of follow-up. Garre's osteomyelitis and radicular cysts associated with deciduous molars are uncommon. Therefore, the purpose of this article was to illustrate a case with Garre's osteomyelitis and a radicular cyst related to the right and left mandibular deciduous second molars, respectively. A brief review of literature was also provided.