The known interaction between the immune system and the hypothalamic-pituitary-adrenal axis led us to explore the interrelation between magnetic resonance imaging findings and the hypothalamic-pituitary-adrenal axis activity in 53 multiple sclerosis patients. The cortisol release induced by the dexamethasone-corticotropin-releasing hormone test was negatively associated with the presence and number of gadolinium-enhancing lesions and positively associated with ventricular size. This finding suggests a protective effect of the hypothalamic- pituitary-adrenal drive on acute lesional inflammation in multiple sclerosis, probably by limiting immune overshoot. In contrast, the nature of the correlation between hypothalamic-pituitary-adrenal hyperdrive and brain atrophy remains to be determined.