objectives: to describe the clinical outcomes and thrombotic events in a series of critically ill cancer patients positive for antiphospholipid (apl) antibodies. design: retrospective case series study. setting: medical-surgical oncologic intensive care unit (icu). patients and participants: eighteen patients with sirs/sepsis and multiple organ failure (mof) and positive for apl antibodies, included over a 10-month period. interventions: none measurements and results: apl antibodies and coagulation parameters were measured up to 48 hours after the occurrence of acrocyanosis or arterial/venous thrombotic events. when current criteria for the diagnosis of apl syndrome were applied, 16 patients met the criteria for "probable" and two patients had a definite diagnosis of apl syndrome in its catastrophic form (caps). acrocyanosis, arterial events and venous thrombosis were present in eighteen, nine and five patients, respectively. sepsis, cancer and major surgery were the main precipitating factors. all patients developed mof during the icu stay, with a hospital mortality rate of 72% (13/18). five patients were discharged from the hospital. there were three survivors at 90 days of follow-up. new measurements of lupus anticoagulant (lac) antibodies were performed in these three survivors and one patient still tested positive for these antibodies. conclusions: in this small series of patients, we observed a high frequency of auto-antibodies and micro- and macro-vascular thrombotic events in critically ill cancer patients. the coexistence of sepsis or sirs and apl antibodies was often associated with mof and death. more studies are necessary to determine the pathophysiological significance of antiphospholipid antibodies in severely ill cancer patients.