High nasal airway resistance (NAR) has been reported in Marfan's syndrome, and this appears to contribute to the development of obstructive sleep apnoea in these patients. The cause of high NAR in Marfan's syndrome is unknown, but these patients characteristically have a narrow maxilla, which could have an influence on nasal dimensions. The aim of this study was to define the mechanism(s) mediating high NAR in Marfan's syndrome. Five patients with Marfan's syndrome (mean age 29+/-4 (SEM) years) were compared with an equivalent number of normal control subjects (31+/-1 years). NAR was measured by posterior rhinomanometry, before and after topical decongestant, nasal stenting, or both. Dental impressions were taken to evaluate maxillary arch morphology, allowing measurement of the following lateral distances: inter-canine (ICD), inter-premolar (IPD), and inter-molar (IMD). NAR (at a flow of 500 ccm/s) was considerably higher in patients compared with controls at baseline (0.93+/-0.08 vs 0.35+/-0.08 Pa/ccm/s, p < 0.001), and following decongestant and/or stenting. The maxillary arch was considerably narrower in patients. There were strong inverse correlations between the lateral maxillary dimensions and NAR after nasal decongestant, with or without stenting. These results indicate a strong association between maxillary width and NAR, and suggest that maxillary constriction is the dominant mechanism for the high NAR in Marfan's syndrome. The therapeutic implications of this finding warrant further investigation.