With a view to assessing genotype-to-phenotype correlations in cystic fibrosis (CF), the clinical presentation of CF children from the United Arab Emirates (UAE) who were homozygous for cystic fibrosis transmembrane conductance regulator (CFTR) mutation S549R(T-->G was investigated. This mutation is localized in intron 11 (nucleotide binding domain 1 of the CFTR protein) and had so far been described as a private mutation only. The associations between the R549/R549 genotype and 20 outcome variables, including age at diagnosis, sweat chloride concentrations, growth percentiles, meconium ileus, pancreatic sufficiency, pulmonary disease, associated complications and micro-organism colonization were examined in a group of 15 CF children (9 females and 6 males). Mean current age and age at diagnosis were both low (5.4+/-3.5 and 1.0+/-1.1 yrs, respectively). Although none of the 15 CF patients had presented with meconium ileus at birth, all were pancreatic insufficient and had very severe lung disease, with a high rate of Pseudomonas aeruginosa and Staphylococcus aureus. Two patients died during the course of this investigation (one was 5 months and the other, 6 yrs old). The clinical presentation associated with S549R(T-->G) homozygosity in the United Arab Emirates is quite homogeneous and shows an extreme degree and course of cystic fibrosis severity.