The authors report a fatal case of Corynebacterium sp. endocarditis. Corynebacterium spp. are non-sporulating, pleomorphic Gram-positive bacilli. In particular the authors have identified a species of Corynebacterium very closely related to C striatum. This is C simulans. The authors were able to identify the genus and species using various phenotypic tests. Highlighted here is the importance of identifying diphtheroids as a significant pathogen in the appropriate setting and the need to start antibiotic therapy if this is suspected.