Ask Mr. Smarty Plants

Maclura pomifera (osage orange) is dioecious, which means that flowers of both sexes do not appear on the same tree. So, yes, you would need both a male and a female tree. If you are growing the tree in areas where it grows wild, that would not be an issue.

From the Great Plains Nature Center, here is an excellent article on Osage Orange. We have personal experience with this plant, in North Central Texas, which is its native habitat. It was growing on its own, on a property we had purchased. It obviously was a female tree, as it bore fruit. Equally obviously, there must have been a male in the neighborhood, because it bore fruit. While it was an interesting plant for an open property such as we had, we don't think it would be suitable for a residential property, because the fruit was very messy, especially with the squirrels sitting under it tearing the fruit to pieces for the seeds. 

From the page on this plant in our Native Plant Database, here are some excerpts that we think would be of interest to you if you are investigating growing it:

"Native Distribution: The native range uncertain. SW. Arkansas to E. Oklahoma and Texas; widely planted and naturalized in the eastern and northwestern states.
Native Habitat: Prairie, Plains, Meadows, Pastures, Savannahs, Woodlands edge, Opening, Fence rows, Ditches, Ravines, Depressions"

And from the GNPC reference above:

"The trees will be either male or female, and only the females will produce hedge balls. The trees become sexually mature by age 10 and there is no easy way to determine the gender prior to then."

From our Native Plant Image Gallery:

Maclura pomifera

Maclura pomifera

Maclura pomifera

Maclura pomifera