Treatment periods for bacterial meningitis are often very long, and often this prolonged treatment is based on the judgment of its effectiveness by the degree of enhancement on brain magnetic resonance imaging (MRI). In this study, we analyzed the contrast MRI in the acute and recovery phases of bacterial meningitis in twelve patients, and graded the contrast level of the subdural space and subarachnoid space separately. While the contrast level of the subarachnoid space increased with time in 4 cases, that of the subdural space increased in 10 cases, and 9 of them revealed a good prognosis without continuation of the treatment. These findings indicate that increased contrast level of the subdural space is common in the recovery phase of bacterial meningitis, and that repetitive MRI investigation is not valuable to determine the duration of treatment.