The dentigerous cyst is generally discovered during routine radiographic examination although it may be found because of secondary infection. Although the patient described in this report had symptoms of infection, discovery of the lesion was late in the course of development of the cyst as it grew to a large size within the antral cavity without causing external expansion. The panoramic radiograph is an excellent method to screen for central jaw disease but may not allow adequate assessment of processes involving the maxillary sinuses. As illustrated by this report, when the absence of a third molar is not explained by the patient's history or by the panoramic radiograph, additional radiographs are essential to specifically visualize the sinuses and upper middle part of the face for accurate diagnosis.