A number of studies examining the effects of deliberative citizen forums have found that citizens taking part in deliberative processes experience changes in their policy attitudes. However, it remains unclear why these opinion changes occur, since most studies pay little attention to the communicative exchange that is expected to cause the observed changes. Within deliberative theory, there is an expectation that reasonable individuals should be amenable to changing their preferences as a result of the reflection induced by the deliberative process. However, apart from a few recent studies, there has been little empirical research that directly examines how the quality of the communication affects opinion change. This article fills this gap by examining what factors help explain the opinion changes that occur in citizen deliberation. To do this, the article uses data from a mini-public organized in Turku, Finland, concerning the use of nuclear power. First, the extent and nature of the opinion changes that occurred as a result of the deliberation are established. Following this, the article examines the explanatory powers of a number of potential explanations: deliberative reasoning, sociodemographic inequalities and issue awareness. The results suggest that both deliberative reasoning and issue awareness are significant predictors, meaning there is no single explanation for opinion changes.