Trousseau is considered to be the first to have recognised a relation between venous thromboembolism (VTE) and malignancy. Illtyd James and Matheson in 1935 were the first in the Anglo-Saxon literature, at least to our knowledge, to report the observation of a patient with occult cancer at time of his venous thrombosis. Meanwhile, cancer has become an established risk factor for VTE. The prevalence of concomitant cancer in patients presenting with VTE varies considerably between the studies due to differences in, for instance, threshold of suspicion, screening methods, and characteristics of the patients like age. A consistent observation is the low prevalence of concomitant cancer in patients with secondary thrombosis, comparable to the prevalence in the general population. A 3-19-fold increase in prevalence of concomitant cancer has been reported in patients presenting with an idiopathic VTE. The same applies for occult cancer in patients with secondary and idiopathic VTE. The prevalence of occult cancer in patients with secondary VTE is comparable with the prevalence of cancer in the general population, while the prevalence of occult cancer in patients with idiopathic VTE is 4-10%. It seems possible to detect a substantial number of additional cancer patients, at time of diagnosis of idiopathic VTE, by means of extensive screening. However, results of randomised trials, evaluating the effect on survival rate, are lacking.