Maxillary sinus retention cysts are occasionally found on dental radio­graphs. The objective of this study was to verify the frequency of maxillary sinus retention cysts in consecutive panoramic radiographs from 173 patients (77 males, 96 females) in an orthodontic office. The chi-square test was used for statistical analysis. Ten patients (5.8%) of the total sample presented a maxillary sinus retention cyst. Males had a higher frequency (9.1%) than females (3.1%), but this difference was not significant (P > .05). Overall, the frequency of maxillary sinus retention cysts in orthodontic patients is rather low and does not differ from the general population. World J Orthod 2009;10:e7–e8.