ABSTRACT The reported study investigated the effects of normative factors and metacognitions on opinion expression behavior. It sought to add to the knowledge base by probing the extent to which they operate additively or non-additively. Participants were placed in an online opinion environment and given the choice about whether and how to express something. Perceived minority opinion status, trait-like fear of social isolation, situationally-dependent beliefs about the sanctions one would receive for expressing something, attitude strength, and attitude certainty were measured. The results failed to support a non-additive effect. Rather, three normative factors independently predicted whether participants commented, and attitude certainty solely predicted the directness of participants’ expressions. We speculate that normative beliefs may contribute to participants’ decisions about whether to express something, and metacognitions may contribute to the form of those expressions.