Platelets are small fragments, but they are of crucial importance for the coagulation. The risk of spontaneous bleeding increases when the level of platelets falls below a thrombocyte particle concentration threshold value of 50 x 109/L. In those cases a platelet transfusion might be compulsory. Ongoing research tries to improve the quality of the platelets and to increase the safety of the method used. However, we still need to better understand which factors that affect how patients react upon platelet transfusion. In this study, 100 transfusions performed at Uppsala University Hospital during 2009 were examined. The platelets used had been produced with apheresis followed by pathogen inactivation by Intercept Blood SystemTM. Platelets were counted before and after transfusions and the increase was calculated in purpose to examine how well the patients responded to the platelet transfusions. These values were plotted against platelet storage time in order to examine the possible impact on the result of treatment.