Dentigerous cyst is the most common cyst of the jaw bone in children and adolescents. Dentigerous cyst exhibits no significant symptoms clinically and is usually found through routine radiographic examination. Extensive cyst may cause buccal bony expansion, facial asymmetry and tooth bud displacement. Treatment of dentigerous cyst may be performed by enucleation and marsupialization. This case is to report an extensive cyst in a 8-year-old boy treated by marsupialization to preserve the permanent tooth bud. Long term follow-up showed no recurrence of the dentigerous cyst and the affected permanent teeth were in good alignment.