BacFitBase is a manually curated database of bacterial genes that includes information on their relevance during host infection, as measured by transposon mutagenesis. It contains more than 90,000 entries with information on the contribution of individual genes to bacterial fitness under in vivo infection conditions. The data were collected from 15 different studies where transposon mutagenesis was performed. Overall, BacFITBase includes information on 15 pathogenic bacteria and 5 host vertebrates across 10 different tissues.