Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the central nervous system, in which unknown environmental factors are thought to trigger disease in genetically susceptible persons. Glucocorticoids (GCs) play an important role in controlling chronic inflammatory diseases, like MS. Three polymorphisms in the glucocorticoid receptor (GR) gene (N363S, ER22/23EK and the Bcl I C/G) have been shown to alter glucocorticoid sensitivity, and therefore may influence disease course. We investigated the influence of these polymorphisms on clinical and MRI parameters. The ER22/23EK polymorphism was associated with a more aggressive MS phenotype, measured both clinically and on MRI.