Eighty‐five patients were classified as having definite (n = 34), probable (n = 18), or possible (n = 33) multiple sclerosis using the criterial of Poser. Each Patient had an enhanced computed tomographic examination, and most had cerebrospinal fluid and evoked response studies at the same time. Abnormalities including focal decreased brain density, abnormal enhancement, and cerebrospinal fluid space enlargement were found in 62% of patients (85% of those with definite, 39% of those with probable, and 52% of those with possible multiple sclerosis), and abnormal enhancing areas were demonstrated in 29% (44% of those with definite, 17% of those with probable, and 21% of those with possible disease). In the subgroup of patients with definite multiple sclerosis and recent clinical exacerbation (within the prior 8 weeks), abnormal enhancement was present in 89%. There was a strong correlation between clinical exacerbation and abnormal contrast enchancement. Cerebrospinal fluid studies (IgG, white blood cell count, total protein) had no correlation with exacerbation or abnormal enhancement. Maps of low‐density and enhancing areas were similar to those previously described in postmortem studies. Computed tomography thus provides an in vivo, objective, and anatomically specific map of the brain parenchyma and the integrity of the blood‐brain barrier that is useful in research studies evaluating the treatment of multiple sclerosis. It is also useful in patients in whom the diagnosis of multiple sclerosis is suspected but not certain on the basis of clinical and laboratory evaluation.