Encouraging organizations to be more open has been a key issue in contemporary debates over nonprofit accountability. However, our understanding of what motivates organizations to the disclosure decision is weak. We aim to enhance our understanding of this critical issue by developing and testing a model of the determinants of voluntary disclosure decision making, using data gathered on the population of not-for-profit medical institutions in Taiwan during a period where the government encouraged—but did not require—disclosure on a centralized website. As a result, we are able to conduct a “natural experiment” of the voluntary disclosure behavior of an important population of non-donor-dependent organizations. We find voluntary disclosure is more likely in organizations that are smaller, have lower debt/asset ratios, and are run by larger boards with more inside members. Our data suggest that, from a policy perspective, voluntary disclosure regimes are not an especially effective means of promoting public accountability.