Four of five patients with asymptomatic small or moderate-size pulmonary arteriovenous malformation (PAVM) presented with a paradoxical embolus and stroke. In these patients chest radiographic findings were subtle and arterial hypoxemia provided the real clue to diagnosis. Computed tomography (CT) and cerebral arteriography confirmed embolic occlusion in four of five patients. Careful family screening including posteroanterior (PA) and lateral chest radiographs and arterial oxygen determinations in sitting or standing positions are recommended for early detection of asymptomatic patients with PAVM. Early therapeutic intervention (with balloon embolotherapy) is recommended to avoid paradoxical embolization.