Two studies (Gerlach et al. 2000; Gerlach et al. 2002) described the impact of factor XIII on the risk of prospective hemorrhage for patients undergoing craniotomy. Since then, factor XIII is measured and substituted in various centers. Few reports support the idea of factor XIII being involved in the formation of deep venous thrombosis and pulmonary embolism. In this prospective observational study, patients undergoing craniotomy for brain tumors or vascular lesions are investigated concerning the incidence of postoperative pulmonary embolism in respect of possible risk factors (factor XIII activity levels, standard coagulation parameters, tumor entity, blood loss).