It is frequent meeting people sent to perform a tilt test suffering from a single or such isolated syncope that occur very occasionally during the patient's life. We ask ourselves how these people differ from those who never have syncopes. Methods: We performed tilt test in 104 patients who suffer a single or maximum 5 syncopes from any cause during their lifetimes. We try to explain how different predisposing factors act to provoke syncope. Results: We found differences between cases and controls in inheritance of syncopes, joint hypermobility, venous pooling during tilt test, food intake, use of drugs, stress and emotion as a trigger for syncope. Conclusions: Patients with single or occasional syncope have an organic predisposition (inheritance-joint hypermobility-failure in the baroreflexes, some neurological diseases, etc.) to present syncopes, but syncopes do not occur unless it is added simultaneously an environmental factor, which acts as a trigger (prolonged standing up-stress, pain and emotion-dehydration-drugs-abundant food, etc.) that is why these episodes are so rare.