tThe current study is the first to longitudinally investigate the reciprocal relationship between onlinehealth information seeking and health anxiety, i.e., cyberchondria. Expectations were that health anx-ious individuals who go online to find health information, experience an increase in health anxiety,which in turn will reinforce online seeking. A 4-wave longitudinal survey study among 5322 respon-dents aged 16–93 was conducted. Our results showed that individuals who are more health anxious thanothers, search online for health information more. Moreover, the results provided initial evidence forthe expected reciprocal relationship between health anxiety and online health information seeking inrespondents with non-clinical levels of health anxiety at the start of the study. However, this reciprocalrelationship could not be found in a subsample of clinically health anxious individuals. Although for theseindividuals online health information seeking did not seem to exacerbate health anxiety levels, it mightstill serve as a maintaining factor of clinical health anxiety.