Purpose: To examine age and gender differences in the fatty marrow changes that occur in the proximal metaphysis of the femur six months and six years after corticosteroid therapy in patients with severe acute respiratory syndrome (SARS). Methods: A total of 151 SARS patients were included in this study, 122 who underwent corticosteroid therapy (+CS group) and 29 who did not (control group). Magnetic resonance imaging (MRI) was performed for all patients approximately 6 months and 6 years after the onset of SARS. Index of marrow conversion (IMC) percentages for the proximal metaphysis of the femur were determined from the midsection of the proximal femur on T1-weighted coronal MRI scans obtained for all patients at both timepoints, and these were compared. Results: Fatty marrow was observed to increase significantly in the proximal metaphysis of the femur for patients that received corticosteroid therapy compared to the control group. Moreover, the IMC percentages for male patients were significantly higher than for the female patients six months after corticosteroid therapy. The IMC values for patients aged 20–29 years and 30–39 years were also higher than those of patients who were 40–49 years of age (p = 0.012 and p = 0.069, respectively) based on the six month MRI scans examined. However, these differences did not exist six years later. Conclusions: Both male SARS patients, and younger SARS patients of both genders, were more susceptible to corticosteroid treatments and experienced an increase in fatty marrow conversion.