Newborn screening for the inborn error of metabolism, classical galactosaemia prevents life-threatening complications in the neonatal period. It does not however influence the development of long-term complications and the complex pathophysiology of this rare disease remains poorly understood. The objective of this study was to report the development of a healthcare database (using Distiller Version 2.1) to review the epidemiology of classical galactosaemia in Ireland since initiation of newborn screening in 1972 and the long-term clinical outcomes of all patients attending the National Centre for Inherited Metabolic Disorders (NCIMD). Since 1982, the average live birth incidence rate of classical galactosaemia in the total Irish population was approximately 1:16,476 births. This reflects a high incidence in the Irish 'Traveller' population, with an estimated birth incidence of 1:33,917 in the non-Traveller Irish population. Despite early initiation of treatment (dietary galactose restriction), the long-term outcomes of classical galactosaemia in the Irish patient population are poor; 30.6 % of patients ≥ 6 yrs have IQs <70, 49.6 % of patients ≥ 2.5 yrs have speech or language impairments and 91.2 % of females ≥ 13 yrs suffer from hypergonadotrophic hypogonadism (HH) possibly leading to decreased fertility. These findings are consistent with the international experience. This emphasizes the requirement for continued clinical research in this complex disorder.