Molecular data are required to improve our understanding of the epidemiology of leptospirosis in Africa and to identify sources of human infection. We applied molecular methods to identify the infecting species and genotypes among patients hospitalized with fever in Tanzania and compared these with genotypes detected among animals in Tanzania to infer potential sources of human infection. We performed real-time PCR to detect the presence of pathogenic in acute-phase plasma, serum, and urine samples obtained from study participants with serologically confirmed leptospirosis and participants who had died with febrile illness. blood culture was also performed. In positive specimens, we performed species-specific PCR and compared participant sequences with reference sequences and sequences previously obtained from animals in Tanzania. We detected DNA in four (3.6%) of 111 participant blood samples. We detected (one participant, 25.0%), (one participant, 25.0%), and (one participant, 25.0%) (one [25%] undetermined). Phylogenetic comparison of sequence from the and genotypes detected from participants was closely related to but distinct from genotypes detected among local livestock species. Our results indicate that a diverse range of species is causing human infection. Although our analysis suggests a close relationship between genotypes found in people and livestock, continued efforts are needed to obtain more genetic material from human leptospirosis cases to help prioritize species and genotypes for control.