Hfq is an RNA-binding protein that interacts with both small untranslated RNAs (sRNAs) and mRNAs to modulate gene expression post-transcriptionally. In Escherichia coli and Salmonella typhimurium, Hfq is required for efficient expression of the stationary phase sigma factor σS, and consequently is critical for Salmonella virulence. We have found that Hfq is also essential for the virulence of Vibrio cholerae, as strains lacking hfq fail to colonize the suckling mouse intestine. Deletion of the V. cholerae hfq does not prevent production of σS, nor does it prevent expression of TCP, V. cholerae's primary colonization factor. The expression and activity of the alternative sigma factor σE are dramatically increased in a V. cholerae hfq mutant. Comparison of the transcriptome of an hfq mutant with that of an rseA mutant, which also overexpresses σE, revealed that σE controls approximately half the genes found to be upregulated in the hfq mutant. However, increased σE does not appear to account for this strain's reduced virulence. It is likely that sRNAs, in conjunction with Hfq, are critical regulators of V. cholerae pathogenicity.