The purpose of this report is to describe a treatment method of dentigerous cyst associated with unerupted permanent teeth in mixed dentition patients. In our cases, extraction of infected primary teeth was followed by decompression of the cyst. At the same time, parts of the cystic walls were sent for histopathological examination. Decompression was performed by inserting a rubber tube into the cystic cavity through the extraction socket. The cystic cavity was kept open by means of vigorous use of a syringe by patient. Postoperative panoramic radiograph was taken bimonthly. After $5{sim}12$ months, the impacted permanent teeth were erupted on the desired position. All cases presented favorable result. By extracting the infected primary teeth, and opening the cyst for continuous drainage, it was possible to achieve spontaneous eruption of the involved permanent teeth into the proper position. In all our cases, there was no sign or symptom of recurrence of the cyst up to postoperative 18 months.