Photodynamic diagnosis could be a useful tool for improving the diagnostic yield of tumor biopsy, especially for mesothelioma tumors that are sclerotic and particularly hypocellular. For PDD, the use of low doses of a sensitizing drug, such as 5-ALA, must be investigated further. The initial results of 5-ALA-mediated PDD are promising. The role, if any, for PDT in the treatment of mesothelioma has yet to be established. The number of centers exploring this technology is limited because the procedure is labor intensive and requires not only specialized equipment but also physician support. The number of patients treated in the different trials is small, and no definitive conclusions can be drawn. Further complicating the interpretation of published results is the number of variables (i.e., type of sensitizer, light dose, drug dose, drug light interval, methods of light measurement, technique of light delivery, surgical debulking techniques), which differ between studies. Most reports are phase I and II studies. The final outcome of these studies with respect to survival is of limited value. The only phase III study, which was performed with an earlier generation photosensitizer, reported no advantage to the use of PDT in combination with surgery and immunochemotherapy. To date, the most that can be said is that intraoperative PDT can be performed safely in experienced centers and that there are some encouraging results, especially in patients with stages I and II MPM, particularly with the newer generation photosensitizers. One attractive aspect of this adjuvant treatment is that PDT, as opposed to some of the other adjuvant treatments combined with surgery, may offer the option of effecting adequate tumor debulking with a pulmonary-sparing procedure.