Pancreatic islet fibrosis with varying degrees of islet cell hyperplasia or islet effacement was diagnosed histologically in 19 rock hyraxes (Procavia capensis) from seven zoological parks. Some, but not all, affected hyraxes were from a common lineage. The condition was associated with apparent hyperglycemia in seven and diabetes mellitus in two. Immunohistochemistry revealed hyperplasia of beta, alpha, and delta cells proportional to the degree of the fibrosis. Electron microscopy revealed collagen deposition and fibroplasia within and around the islets. Special stains and electron microscopy were negative for the presence of amyloid. Beta cell depletion was never identified. The condition has morphologic features that resemble islet fibrosis of human infants born to diabetic mothers.