In this article, we test an alternative approach to creating a counterfactual basis for estimating individual and average treatment effects. Instead of using control/comparison groups or before-measures, the so-called Counterfactual as Self-Estimated by Program Participants (CSEPP) relies on program participants' self-estimations of their own counterfactual at the end of an intervention. In an empirical study, a randomized experiment was employed as a benchmark to examine the performance of the CSEPP. The results suggest that the approach is capable of delivering comparatively reliable estimates of short- and midterm effects on behavioral intentions and attitudes. With regard to the estimation of treatment effects on self-reported behavior, however, the findings are more ambiguous.