This study explored the cost-effectiveness and return-on-investment of a combined social and physical environmental worksite health promotion program compared with usual practice, and of both intervention conditions separately. Participants were randomized to the combined intervention (n = 92), social environmental intervention (n = 118), physical environmental intervention (n = 96), or control group (n = 106). The social environmental intervention consisted of group motivational interviewing and the physical environmental intervention of workplace modifications. Both interventions were aimed at improving physical activity and relaxation. Effects included need for recovery (NFR), general vitality and job satisfaction. Cost-effectiveness analyses were performed from the societal and employer's perspective, and return-on-investment analyses from the employer's perspective. Compared with usual practice, the combined intervention was significantly more effective in improving NFR (-8.4;95% CI:-14.6;-2.2) and significantly more expensive to the employer (3102; 95%CI:598;5969). All other between-group differences were non-significant. For NFR, the combined intervention became the preferred option at willingness-to-pays of ≥€170/point improvement (society) and ≥€300/point improvement (employer). For general vitality and job satisfaction, the interventions' maximum probabilities of cost-effective were low (≤0.55). All interventions had a negative return-on-investment. The combined intervention may be cost-effective for NFR depending on the decision-makers' willingness-to-pay. Both separate interventions are not cost-effective for NFR. All interventions were neither cost-effective for general vitality and job satisfaction, nor cost-saving to the employer.