This paper describes the estimation of probability of detection (POD) for a vibrothermography inspection procedure. The results are based on a large scale experiment on specimens with two different kinds of metal containing fatigue cracks. The specimens were tested independently at three inspection sites: Iowa State University (ISU), Pratt and Whitney (PW) and General Electric (GE). Despite the substantially different vibrothermography configurations and experimental measurement responses, the estimated PODs as function of crack length and dynamic stress were similar for all three inspection sites, which make quantitative POD comparisons possible across different inspection sites.