Aplastic anaemia in adults is usually acquired, but rarely constitutional types of bone marrow failure can occur late in life. We assessed two families with onset of pancytopenia in adults and detected two novel point mutations in the telomerase RNA gene (TERC) in each family. This gene is abnormal in some kindreds with dyskeratosis congenita. Individuals in our families with mutated TERC did not have physical signs of dyskeratosis congenita, and their blood counts were nearly normal, but all had severely shortened telomeres, reduced haemopoietic function, and raised serum erythropoietin and thrombopoietin. Bone marrow failure of variable severity due to dyskeratosis congenita, historically characterised by associated physical anomalies and early pancytopenia, may be present in otherwise phenotypically normal adults, and can masquerade as acquired aplastic anaemia.