Stroke is a rare disorder in childhood. The majority of these cases is of an ischemic nature. In spite of the long list of known causes, many strokes remain undetermined, so-called cryptogenic strokes. Increasing evidence indicates that, in the young adults, many cases of cryptogenic stroke are presumably due to paradoxical embolism. In childhood, this is usually not considered, unless in the context of a complex cyanotic heart disease. We present two cases, a 6-year-old boy and an 11-year-old girl who had an episode of cerebral ischemia documented by MRI, and in whom the only anomaly found was a patent foramen ovale (PFO) with intermittent left to right shunt at rest, but with a large right to left shunt during the Valsalva maneuvre. We assumed that, in our cases, in the absence of identifiable causes, the cerebral ischemia was most likely due to paradoxical embolism through the PFO. Of course, as in the adult, the paradoxical embolism could not be proved, but in our opinion it remains the most concrete possibility. Therefore, in presence of a cryptogenic stroke, a PFO should be investigated also in children.