The echocardiographic features of a surgically confirmed case of an aneurysm of the inter-atrial septum presenting as a persistent right atrial lesion were described. The lesion appeared cystic and could be differentiated from solid tumours. In contrast to other reported cases of smaller aneurysms, the lesion in this patient remained in the right atrium and did not show any phasic variation during the respiratory cycle because of its larger size. A review of the reported echocardiographic features of intra-cavitary right atrial tumours and pseudotumours was made. This highlighted distinguishing features that could be used in the differential diagnosis of space-occupying lesion within the right atrium.