The COVID-19 pandemic has brought unprecedented situations (government lockdowns, quarantines, etc.) and stressors (a seemingly “phantom” virus that can be lurking anywhere) causing uncertainty for the future, uncontrollable and unpredictable situations. It appears that especially during times of uncertainty and high stress, conspiracy theories flourish and these can affect the way individuals behave, especially in response to governmental recommendations for social isolation and quarantine. Psychological flexibility, we hypothesized, may act as a protective factor in the relation between COVID-19 distress, conspiracy theory beliefs and consequent behaving. In this respect, the aim of this paper was to examine how conspiracy theory beliefs, COVID-19 distress, adherence behavior, and psychological flexibility interact. Participants were 1001 individuals (802 women; Mage=35.59years, SD= 10.07), who completed an online survey approximately one month after the first governmental measures of self-isolation and quarantine were enforced. Psychological flexibility was found to mediate the relation between conspiracy theory beliefs and compliance behavior. Further, being highly stressed appeared to increase the probability that a person will believe conspiracy theories, while such beliefs influenced whether a person would follow public health recommendations. Psychological flexibility appeared to be a protective factor at low and moderate distress levels. However, at high levels of COVID-19 distress, individuals prone to conspiracy theory beliefs would be less likely to conform to governmental public health recommendations irrespective of their psychological flexibility levels.