Combined X-ray topographic and phase-contrast micrographic studies of natural diamond octahedral faces show that pyramidal trigons are always associated with dislocation outcrops. No dislocations outcrop at flat-bottomed trigons. On the other hand, absence of trigons does not necessarily imply absence of outcropping dislocations. The X-ray evidence strongly supports the etch-pit hypothesis for the origin of trigons. A dependence of trigon pit slope upon the Burgers vector orientation of its associated dislocation was not conclusively demonstrated.