The gut microbiota has been implicated in the development of IBD, but little is known about the role of the viral intestinal communities. A new study demonstrates that ulcerative colitis is characterized by substantial changes in the mucosal virome, namely a high abundance of Caudovirales bacteriophages but decreased diversity, richness and evenness of mucosal Caudovirales in comparison with healthy individuals. Deep metagenomic sequencing of viral-like particle preparations and bacterial 16S ribosomal RNA sequencing were performed on rectal mucosal samples from 91 individuals with ulcerative colitis and 76 healthy individuals as controls. Sequencing data were then correlated with patient metadata. Additional analysis revealed that this altered mucosal virome was associated with intestinal inflammation and altered virulence functions and interkingdom correlations between mucosal viruses and bacteria in the context of ulcerative colitis.