To evaluate whether the presence of antiphospholipid antibodies in lymphoma patients influences their response to treatment, and their rate of thromboembolic complications, we followed up 100 consecutive patients with different lymphomas, who underwent measurement of lupus anticoagulants and anticardiolipin antibodies at diagnosis. In all, 27 patients had lupus anticoagulants and/or anticardiolipin antibodies. This prevalence was significantly higher than in a group of 100 age- and sex-matched normal control subjects (8%; P=0.0008, odds ratio 4.25, 95% confidence interval, 1.82-9.92). At diagnosis, antiphospholipid-positive and -negative patients were similar with respect to age, sex, type and staging of lymphomas. During follow-up, the rate of thrombosis was significantly higher in patients with (5.1% patients/year) than without (0.75% patients/year) antiphospholipid antibodies. The two groups were similar with respect to relapse and death rate. In conclusion, antiphospholipid antibodies are associated with lymphomas. Their determination is useful to identify patients at high risk to develop thrombotic complications, but not to predict treatment outcome or disease prognosis.