This paper presents two studies on the development and validation of a ten-item scale of epistemic vice and the relationship between epistemic vice and misinformation and fake news. Epistemic vices have been defined as character traits that interfere with acquiring, maintaining, and transmitting knowledge. Examples of epistemic vice are gullibility and indifference to knowledge. It has been hypothesized that epistemically vicious people are especially susceptible to misinformation and conspiracy theories. We conducted one exploratory and one confirmatory observational survey study on Amazon Mechanical Turk among people living in the United States (total N = 1737). We show that two psychological traits underlie the range of epistemic vices that we investigated: indifference to truth and rigidity. Indifference manifests itself in a lack of motivation to find the truth. Rigidity manifests itself in being insensitive to evidence. We develop a scale to measure epistemic vice with the subscales indifference and rigidity. The Epistemic Vice Scale is internally consistent; has good convergent, divergent, and discriminant validity; and is strongly associated with the endorsement of misinformation and conspiracy theories. Epistemic vice explains additional variance in the endorsement of misinformation and conspiracy theories over and above demographic and related psychological concepts and shows medium to large effect sizes across outcome measures. We demonstrate that epistemic vice differs from existing psychological constructs, and show that the scale can explain individual differences in dealing with misinformation and conspiracy theories. We conclude that epistemic vice might contribute to “postfactive” ways of thinking.