Many prognostic factors have been described in malignant mesothelioma, but only a limited number has been validated by prospective, confirmatory studies. These include performance status, histology, weight loss and leucocyte count. Their value as predictors of patient survival in malignant mesothelioma is limited, as is their role in current clinical practice. At this moment their main importance is their application in clinical studies, which allows a better delineation of the patient group to which the study results can be applied to and a more accurate comparison between different studies. The biological prognostic factors need confirmation by larger prospective trials and should be analysed with respect to the existing prognostic factors. In the future, their use might not be limited to the prediction of the patient survival but direct the development of new therapies and extend to the molecular prediction of tumour response.