Morphological variability is a widespread but poorly understood characteristic of many colonial animals. In this study morphologic variation in Montastrea cavernosa (Linnaeus 1767) from northeastern Brazil is examined. Colonies were collected from three depths: 0–5, 10–15 and 15–20 m at the Abrolhos reefs (Bahia state), and from a single depth (0–5 m) at Tamandare (Pernambuco state). Fifteen measurements or counts were made on each sample. They include the most important characteristics commonly used to separate species in the family Faviidae. The results of statistical analyses show that almost every character studied varies. Between colonies, localities and depth classes, the most variable features are the spacing of corallites, the diameter of corallite, the height of theca and of outer columella, the thickness of first cycle septa, the length of first cycle costae, and the thickness of fourth cycle costae. Canonical discriminant analyses show that the samples from 0–5 m are the most widely separated from samples collected at the other depth classes. Variability within populations is greater than between, but both are significant. Montastrea cavernosa in Brazil is characterized by high morphological variability and polymorphism within populations and cannot be completely explained by environmental variables.