The objective of this paper is to investigate the long-term outcome of primary antiphospholipid syndrome (APS) in the paediatric age. The features of unselected patients with primary APS who had disease onset before the age of 16 years were retrospectively analysed in three Italian referralcentres. Clinical and laboratory manifestations were assessed to establish whether, at the end of follow-up, the final diagnosis was still primary APS or whether they had developed definite SLE or lupus-like syndrome. Fourteen patients, nine boys and five girls, who had the presenting clinical manifestation of APS between three and 13 years of age (median nine years) and were followed for two to 16 years (median six years). Six patients presented with deep vein thrombosis, five with cerebral stroke, two with peripheral artery occlusion and onewith myocardial infarction. During follow-up, four patients had one or more recurrences of vascular thrombosis. At last observation, 10 patients could still be classified as having primary APS, two had developed SLE, one lupus-like syndrome and one Hodgkin's lymphoma. In conclusion; our analysis suggests that some children who present with the features of primary APS may progress to develop SLE or lupus-like syndrome.