As with the monument of Ozymandias, little remains today of the fabulous Balbus complex. What remains is mostly hidden below ground in cellars and wells; only the exedra or apse of the crypta remains visible, partially standing with its six piers set in a semicircle before the arcades of the eastern side of the portico. These cannot reveal the splendor with which Balbus realized his intentions nor evidence the contribution this theater made to Augustus' ambitious building program. In addition, physical evidence is confusing, as the site was continuously overbuilt, destroyed, and transformed by new use from 80 BCE onward. Without contemporary texts, it is impossible, even with sophisticated archaeological excavation, to discover the elements of the original building much beyond its foundation.

The Theater and Crypta were built of large travertine and tufa blocks. The cavea, which had support walls of concrete faced in opus reticulatum, measures close to 100 yards in diameter and is reported in the the 4th century Regionary Catalogue to have 11, 500 loca (i.e., space for some 7, 700 spectators). Pliny the Elder reports that four moderately sized onyx marble columns, which excited widespread admiration at the time for their costliness, decorated the stage facade (Historia Naturalis 36.60), which is assumed to have risen to the height of the cavea. Although some believe that the external facade of the theater resembled that of the Theater of Marcellus, with rising tiers of orders, surrounding archways, and niches for statues, there is no evidence for the original design.