The cerebellum of mormyrid electric fish is large and unusually regular in its histological structure. We have examined the morphology of cellular elements in the central lobes of the mormyrid cerebellum. We have used intracellular injection of biocytin to determine the morphology of cells with somas in the cortex, and we have used extracellular placement of anterograde tracers in the inferior olive to label climbing fibers. Our results confirm previous Golgi studies and extend them by providing a more complete description of axonal trajectories. Most Purkinje cells in mormyrids and other actinopterygian fishes are interneurons that terminate locally in the cortex on efferent neurons that are equivalent to cerebellar nucleus cells in mammals. We confirm the markedly sagittal distribution of the fan-like dendrites of Purkinje cells, efferent cells, and molecular layer interneurons. We show that Purkinje cell axons extend further than was previously thought in the sagittal plane. We show that climbing fibers are distributed in narrow sagittal strips and that these fibers terminate exclusively in the ganglionic layer below the molecular layer where parallel fibers terminate. Our results together with those of others show that the central lobes of the mormyrid cerebellum, similar to the mammalian cerebellum, are composed of sagittally oriented modules made up of Purkinje cells, climbing fibers, molecular layer interneurons, and cerebellar efferent cells (cerebellar nucleus cells in mammals) that Purkinje cells inhibit. This modular organization is more apparent and more sharply defined in the mormyrid than in the mammal.