A thin, filamentous, non-motile, aerotolerant, anaerobic, gram-negative bacterium was isolated from the blood of a 46-year-old man who was diagnosed as having acute myeloid leukemia. The organism had a positive catalase reaction but was negative in indole and oxidase tests. A commercially available system failed to identify the bacterium, but 16S rRNA gene sequencing showed it to be most closely related (97% similarity) to a recently isolated Leptotrichia sp. The DNA base composition was 29.7% mol G+C, and the organism produced lactate as the sole end-product of glucose fermentation. These data indicate the isolate is a new species of Leptotrichia for which the name Leptotrichia trevisanii sp. nov. is proposed.