Severe Aplastic Anaemia (SAA) is a rare benign disease but carries a high-mortality rate unless treated in a specialised centre. Overwhelming laboratory and clinical evidence points to an autoimmune pathogenesis; although, the aetiology remains obscure in the majority of cases. The differential diagnosis in older patients is problematical and a diagnosis of hypoplastic myelodysplasia remains difficult. This review points out the difficulty in diagnosis without a specific test. Future research needs to define a specific diagnostic test and refine therapeutic interventions.