Background: Chikungunya virus (CHIKV) outbreak recurrences in Thailand are unpredictable and separated byunexplained and often long silent epidemiological periods that can last for several years. These silent periods could beexplained in part by the fact that infection with one CHIKV strain confers lasting natural immunity, even against otherCHIKV strains. In this study we evaluated the persistence of CHIKV-specific neutralizing antibodies in the population ofChumpae District, Khon Kaen Province, nineteen years after a CHIKV outbreak occurred in the same area in 1991.Findings: Overall 39% (44/111) of 111 former patients had neutralizing antibodies reacting against CHIKV ECSAstrain. Consistently high titers of neutralizing antibodies were found in 75% (33/44) of all positively-reacting sera,70% of which (23/33) were collected from individuals amongst the >60 years old age group. Although theprevalence found in Pong Haeng village (70%) was significantly higher than the prevalence detected in the NongThum village (14%), control study villages without known previous Chikungunya epidemics had a high Chikungunyaneutralizing antibody prevalence (65%).Conclusions: More than one-third of the pre-exposed population had persisting natural immunity that was morelikely boosted by recent and repetitive exposure to the emerging ECSA CHIKV in Thailand. Also, Chikungunyavirus appears to largely circulate in the country with a great variability appears between villages or area probablyassociated with the vector abundance and efficiency. Altogether these results show a potential for a lifelongimmunity against CHIKV. Given the rapid spread of the highly pathogenic ECSA strain in Southern Thailand, thedevelopment of CHIK vaccine is strongly recommended.