The results of a survey and an experiment show that experiential uncertainty—people's experience of uncertainty in risk contexts—plays a moderating role in individuals’ risk-related demand for government regulation and trust in risk-managing government institutions. First, descriptions of risks were presented to respondents in a survey (N = 1,017) and their reactions to questions about experiential uncertainty, risk perception, and demand for government regulation were measured, as well as levels of risk-specific knowledge. When experiential uncertainty was high, risk perceptions had a positive relationship with demand for government regulation of risk; no such relationship showed under low experiential uncertainty. Conversely, when people experience little experiential uncertainty, having more knowledge about the risk topic involved was associated with a weaker demand for government regulation of risk. For people experiencing uncertainty, this relationship between knowledge and demand for regulation did not emerge. Second, in an experiment (N = 120), experiential uncertainty and openness in risk communication were manipulated to investigate effects on trust. In the uncertainty condition, the results showed that open versus nonopen government communication about Q-fever—a zoonosis—led to higher levels of trust in the government agency, but not in in the control condition. Altogether, this research suggests that only when people experience relatively little uncertainty about the risk, knowledge provision may preclude them from demanding government action. Also, only when persons experience uncertainty are stronger risk perceptions associated with a demand for government regulation, and they are affected by openness of risk communication in forming institutional trust.