Screening of unselected university students in the Sultanate of Oman revealed an overall frequency of glucose-6-phosphate dehydrogenase (G6PD) deficiency of 26% in males. Samples from 23 G6PD-deficient individuals (a random sub-sample of the student population), were characterised biochemically and at the molecular level. Of 20 deficient men, 15 had G6PD Mediterranean, 2 had G6PD Chatham, 1 had G6PD A- and in 2 the mutation is not yet known. Of the 3 G6PD-deficient woman, 2 were homozygous for the G6PD Mediterranean mutation and 1 was a genetic compound, G6PD Mediterranean/G6PD A- (the first report of this genotype). Our findings establish that the G6PD Mediterranean mutation accounts for most cases of G6PD deficiency in Oman. The presence of G6PD A- at a polymorphic frequency can be regarded as evidence of significant gene flow from Africa.