Most social dilemma studies of communication’s effects on cooperation are based on laboratory results with trivial incentives. Studies of real-life social dilemmas with nontrivial rewards are needed to extend the generality of laboratory results. Perceptions of cooperation on a group product (weekly group essay) were examined as a public goods dilemma embedded in a longitudinal study of groups using either face-to-face or computer-mediated communication. Perceptions of cooperation increased over time, whereas measures of group identity did not. No media effect on perceptions of cooperation was observed. Several predictors of late perceptions of cooperation were examined, but only early perception of cooperation was significant. Results are discussed with respect to several current hypotheses regarding communication and cooperation in social dilemmas.