['Recently, the C/T-13910 polymorphism on chromosome 2q21 in North-European populations has been found completely associated with lactase activity and its genetic typing proposed as first-stage screening test for adult hypolactasia. However, the C/T-13910 variant in some sub-Saharan African groups is not a predictor of lactase persistence. In this work, we wanted to verify if in the Mediterranean island of Sardinia, located in Southern Europe, the C/T-13910 polymorphism may be useful or not for the diagnosis of adult type hypolactasia.', 'Validation study of a genetic testing for adult type hypolactasia in Sardinians.', 'Brotzu Hospital and Microcitemico Hospital, Cagliari, Italy.', 'The sample consisted in 84 Sardinian individuals (63 women and 21 men; range 20-73 years) selected from a group of 832 patients.', 'Genetic testing was compared to an improved test obtained by a combination of different breath hydrogen tests and clinical assessment.', 'We found that all 49 individuals with lactose malabsorption, demonstrated by a combination of different breath hydrogen tests and clinical assessment, carried the C/C-13910 genotype associated with lactase non-persistence, 23 individuals with lactose normal absorption carried the C/T-13910 genotype associated with lactase persistence and only one person with the above phenotype showed a discordant C/C-13910 genotype. The genetic testing showed very high sensitivity, specificity, positive and negative predictive values of 100, 95.8, 98 and 100%, respectively.'] Does genetic testing improve the diagnosis of adult type hypolactasia in the Mediterranean population of Sardinia?