The auditory cortex in echolocating bats is one of the best studied in mammals, yet the projections of the thalamus to the different auditory cortical fields have not been systematically analyzed in any bat species. The data of the present study were collected as part of a combined investigation of physiological properties, neuroarchitecture, and chemoarchitecture as well as connectivity of cortical fields in Rhinolophus in order to establish a neuroanatomically and functionally coherent view of the auditory cortex in the horseshoe bat. This paper first describes the neuroanatomic parcellation of the medial geniculate body and then concentrates on the afferent thalamic connections with auditory cortical fields of the temporal region. Deposits of horseradish peroxidase and wheatgerm-agglutinated horseradish peroxidase were made into neurophysiologically characterized locations of temporal auditory cortical fields; i.e., the tonotopically organized primary auditory cortex, a ventral field, and a temporal subdivision of a posterior dorsal field. A clear topographic relationship between thalamic subdivisions and specific cortical areas is demonstrated. The primary auditory cortex receives topographically organized input from the central ventral medial geniculate body. The projection patterns to the temporal subdivision of the posterior dorsal field suggest that it is a "core" field, similar to the posterior fields in the cat. Projections to the ventral field arise primarily from border regions of the ventral medial geniculate body. On the whole, the organization of the medial geniculate body projections to the temporal auditory cortex is quite similar to that described in other mammals, including cat and monkey.