BACKGROUND Idiopathic venous thrombosis (IVT) is associated with occult malignancy in 10% of patients. The Trousseau study investigated whether extensive screening using abdominal and chest computed tomography (CT) scans and mammography in women would decrease mortality, compared with limited screening. Here, the costs and test characteristics of these screening strategies are presented, including true- and false-positive findings, sensitivity and specificity. METHODS All investigations performed because of a suspicion of malignancy in the limited or extensive screening groups were collected. Costs were calculated using Dutch healthcare tariffs. RESULTS A total of 342 and 288 patients with IVT were included in the extensive and the limited screening group, respectively. The prevalences of malignancy and mortality were comparable between these two groups, as were the abnormal findings during routine screening. In 30% of the extensively screened patients, the CT scans or mammography showed abnormalities necessitating further diagnostic work-up; this yielded six malignancies and resulted in a positive predictive value of 6.6%, sensitivity of 33% and specificity of 70%. Mean costs per patient were €165.17 for the routine and €530.92 for the extensive screening. CONCLUSION Screening using CT scans and mammography results in extra costs due to the high percentage of false-positive findings for which a further diagnostic work-up is indicated.