We describe the case of a patient with primary familiar antiphospholipid syndrome and acute myocardial infarction. A previously healthy 15-year-old adolescent was admitted with severe chest pain lasting from 1 hour associated with inferoposterolateral ST-segment elevation. The patient received intravenous thrombolysis. A 2-dimensional echocardiogram revealed an area localized in the basal posterolateral left ventricular myocardium, that was akinetic and abnormally thin throughout the cardiac cycle. Peak creatinine kinase level was 1461 U/I. Subsequent electrocardiogram revealed inferoposterior infarction. Plasma anticardiolipin (aCL) IgG antibodies resulted positive (24 U.GPL) in repeated determinations. A dypiridamole echocardiographic test resulted negative. The patient's parents refused cardiac catheterization. He continues to do well at home 28 months after discharge. The patient's sister is affected by primary antiphospholipid syndrome characterized by recurrent abortion, very low platelet count and lupus anticoagulant positivity. Plasma aCL antibodies resulted positive also in the mother who did not have clinical manifestations.