Background. AAT deficiency is not a rare disease, but one of the most common congenital disorders increasing susceptibility of deficiency individuals to both lung and liver disease as well as other several adverse health effects. Therefore, information on accurate estimates of the magnitude of alpha-1 antitrypsin deficiency in any given country is critical for the development of screening programs for detection, diagnosis, and treatment of those individuals and/or families at risk. Method. Genetic epidemiological studies for alpha-1 antitrypsin deficiency made by others have been used to determine the percentages and estimates of the numbers in each of the five phenotypic classes (PI MS, PI MZ, PI SS, PI SZ, and PI ZZ) of the most common deficiency alleles: PI S and PI Z in each of 69 countries worldwide and also when grouped into 13 major geographic regions. Results. Our studies have demonstrated striking differences between these estimates when comparisons were made in numeric tables, maps and figures. Conclusions. Our studies demonstrated striking differences in the prevalences of both the PIS and PIZ alleles among these 69 countries and the numbers at risk for AAT Deficiency in a given country in specific geographic regions. Data on the prevalence of the two major deficiency alleles as well as the numbers in those phenotypic classes known to be at risk for AAT Deficiency is considered critical for the identification of individuals at risk for adverse health effects associated with AAT Deficiency as well as the treatment and management of those individuals identified in a given country.