Bone marrow failure is believed to be the underlying condition that drives the expansion of the paroxysmal nocturnal haemoglobinuria (PNH) clone. Indeed, circulating PNH blood cells have been identified in patients with acquired aplastic anaemia and with hypoplastic myelodysplasia. Whether PNH blood cells are also present in patients with inherited aplastic anaemia has not been reported. We screened a large group of patients diagnosed with Shwachman-Diamond Syndrome (SDS) for PNH blood cells. None of the patients analysed had detectable circulating PNH blood cells, indicating that bone marrow failure in SDS does not select for PNH progenitor cells.