Cancer associated thrombosis (CAT) has been demonstrated a long time ago and is a frequent comorbid condition. Some risk factors are well established and related to the treatment of cancer: surgery, chemotherapy, radiation therapy, indwelling catheters. Other risk factors depend on tumour type and patient presentation, in particular pancreatic and brain cancer, bed resting and previous venous thrombosis. With the advances in cancer treatment and care, patients with cancer live longer and experience various therapies, sometimes during a long time. There is a need to better define the incidence and prevalence of CAT in the light of new therapeutic strategies and patient survival. This article focuses on the description of incidence and prevalence of CAT in the literature and on the description of risk factors, traditional but also emerging ones.