Employees with low levels of work-related self-efficacy may stand to benefit more from a worksite stress management training (SMT) intervention. However, this low work-related self-efficacy/enhanced SMT benefits effect may be conditional on employees also having high levels of intrinsic work motivation. In the present study, we examined this proposition by testing three-way, or higher order, interaction effects. One hundred and fifty-three U.K. government employees were randomly assigned to a SMT intervention group (n = 68), or to a waiting list control group (n = 85). The SMT group received three half-day training sessions spread over two and a half months. Findings indicated that there were significant overall reductions in psychological strain, emotional exhaustion and depersonalization in the SMT group, in comparison to the control group. Furthermore, there were significant higher order Group (SMT vs. control) x Time 1 Work-Related Self-Efficacy x Time 1 Intrinsic Work Motivation interactions, such that reductions in emotional exhaustion and depersonalization at certain time points were experienced only by those who had low baseline levels of work-related self-efficacy and high baseline levels of intrinsic work motivation. Implications for work-related self-efficacy theory and research and SMT research and practice are discussed.