This prospective, observational and multicentre study assessed the incidence of, and risk factors for, symptomatic venous thrombotic complications after central venous catheter (CVC) positioning in patients with haematological malignancies. A total of 458 consecutive CVC insertions were registered in 416 patients (81.2% of whom had severe thrombocytopenia). Over the observation period (3 months or up to catheter removal), the incidence of events was: CVC-related deep vein thrombosis (DVT), 1.5%; lower limb DVT, 0.4%; pulmonary embolism (PE), 1.3%; fatal PE, 0.6%; CVC-related superficial thrombophlebitis, 3.9%; CVC-occlusion/malfunction of thrombotic origin, 6.1%; major arterial events, 1.1%. Severe bleeding and CVC-related infections were observed in 3.5% and 4.6% of cases respectively. A composite end point (any venous thromboembolism or superficial thrombophlebitis or CVC occlusion/malfunction) was defined in order to consider venous thrombotic events with a significant impact on clinical practice. With this criterion, the overall incidence was 12.0% (2.54 cases/1000 catheter days). No factor helped to predict venous thrombotic complications: only thrombocytopenia was associated with a weak trend for a reduced risk (odds ratio 0.52; 95% confidence interval 0.26-1.07). No severe bleeding was observed in those patients who received antithrombotic prophylaxis. This study shows that the impact on clinical practice of symptomatic CVC-related thrombotic complications is not negligible in patients with haematological malignancies.