The Helicobacter pylori outer membrane protein HopZ is regulated by a phase-variable CT repeat and occurs in two distinct allelic variants. Whole-genome comparisons of isolates from one human volunteer recently provided evidence for in vivo selection for the hopZ ON status. We explored the frequency of sequence variation in hopZ during acute and chronic human infection and studied the association of hopZ with the phylogeographic population structure of H. pylori. hopZ ON variants were cultured from 24 out of 33 volunteers challenged with the hopZ OFF strain BCS 100. Transmission of H. pylori within families was also frequently associated with a status change of hopZ. In contrast, hopZ sequences obtained from 26 sets of sequential isolates from chronically infected individuals showed no changes of status, suggesting that the hopZ status selected during early infection is subsequently stable. Mutations leading to amino acid changes in HopZ occurred more frequently in ON than in OFF status isolates during chronic infection, indicating that sequence changes are more likely the result of positive selection in ON isolates than of a loss of negative selection pressure in OFF isolates. Analysis of 63 isolates from chronically infected individuals revealed no significant correlation of hopZ status with chronic atrophic gastritis. hopZ sequences were obtained from a globally representative collection of 54 H. pylori strains. All H. pylori populations contained hopZ-positive isolates. The data suggest that hopZ has been acquired and split into the two variants before the human migration out of Africa.