[Show abstract][Hide abstract] ABSTRACT: In this study, we sought to describe the community seropositivity of pandemic influenza A (H1N1) in order to estimate immunity shortly after the peak of the first pandemic wave in two provinces in Turkey. This cross-sectional study was conducted in the provinces of Diyarbakir and Ankara, after the first wave of H1N1 incidences in 2009. It was designed to evaluate 276 houses in Diyarbakir and 455 houses in Ankara. Everyone living in these houses was included in the study. An antibody titer of ≥1:40 was considered as a positive result for all age groups. Antibody titers of ≤1:20 were considered as 1 while calculating the log titer and geometric mean. The pandemic H1N1 seropositivity was found to be 24.1% for Ankara and 27.7% for Diyarbakir. In Ankara, seropositivity was statistically associated with the 15-24 age group (odds ratio [OR] = 11.47), pandemic influenza A (H1N1) vaccination (OR = 20.95), and influenza-like illness history (OR = 1.60). In Diyarbakir, H1N1 seropositivity was associated with the 15-24 age group (OR = 8.99) and pandemic influenza A (H1N1) vaccination (OR = 9.94). Because individuals less than 25 years old played an important role in the community transmission of infection and were largely protected against the pandemic influenza A (H1N1) virus, these individuals should be given a high priority for pandemic influenza vaccination in the event of the emergence of another novel pandemic strain.