Abstract: Background Bacteria play a suspected role in the development of several cancer types, and associations between the presence of particular bacteria and prostate cancer have been reported. Objective To provide improved characterisation of the prostate and urine microbiome and to investigate the prognostic potential of the bacteria present. Design, setting, and participants Microbiome profiles were interrogated in sample collections of patient urine (sediment microscopy: n = 318, 16S ribosomal amplicon sequencing: n = 46; and extracellular vesicle RNA-seq: n = 40) and cancer tissue (n = 204). Outcome measurements and statistical analysis Microbiomes were assessed using anaerobic culture, population-level 16S analysis, RNA-seq, and whole genome DNA sequencing. Results and limitations We demonstrate an association between the presence of bacteria in urine sediments and higher D’Amico risk prostate cancer (discovery