When using mobile apps that extensively collect user information, privacy uncertainty, which is consumers’ difficulty in assessing the privacy of the data they entrust to others, is a major concern. Using a simulated app-buying experiment, we find that privacy uncertainty, which is mainly driven by uncertainty about what data are collected and how they are used and protected, is indeed a significant influencer of one’s intentions to use a mobile app and the perceived risk associated with that use, as well as the price a potential consumer is willing to pay for an app. Our results further show that the uncertainty concerning the data collected while using a mobile app drives consumers’ decisions more than the uncertainty regarding data that are collected at the time an app is downloaded. To investigate whether privacy uncertainty continues to be a factor after a consumer has already started using an app, we conducted a survey of users of wellness and personal finance apps. The results indicate that privacy uncertainty is a lingering concern because it continues to influence a user’s intention to continue using an app and the perceived risk associated with that continued use.