alpha-thalassaemia is the most common hereditary anaemia in the world. The majority of Danish immigrants come from countries, where the prevalence of alpha-thalassaemia is high. The aim of this study was to evaluate its frequency in Danish immigrants.Over a year, all samples sent for haemoglobin analysis to our institution from patients with an MCV value < or = 80 fl were examined for an alpha-thalassaemia haplotype by a PCR-based method. All samples were measured, irrespective of the MCV value, over a period of 3 months.We received 239 samples with an MCV m80 fl. Fifty-seven individuals (23.8%) had one or two alpha-thalassaemia haplotypes. In comparison, a beta-thalassaemia trait was found in 44 individuals (18.4%). The -alpha 3.7 haplotype was the most common (91%). Most were heterozygous, but homozygous cases and combinations with an alpha 0-deletion or a haemoglobin variant were also found. The more serious alpha 0-haplotype was found in nine cases (15.8%), among whom four cases had haemoglobin H disease. In 141 patients with MCV values above 80 fl, 11 patients had an alpha(+)-deletion. From these findings and with the knowledge of the prevalence of beta-thalassaemia in immigrants in Denmark, we assessed the prevalence of alpha-thalassaemia to be between 3 and 8%.alpha-thalassemia is no longer a rare, differential diagnosis in Denmark. A national strategy is indicated for prophylactic measures, including screening for the serious alpha 0-deletion and prenatal diagnosis in accordance with international recommendations.