Background & Objectives: Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is a clinical and radiological syndrome with a lesion in splenium of the corpus callosum. This lesion is typically detected in the corpus callosum with magnetic resonance imaging (MRI) and usually disappears within a few weeks. The clinical and radiological features of MERS were evaluated for this study. Methods: Twelve patients were included in the study. They were treated between 2018 and 2021 years. The patients’ demographic and clinical features, laboratory data, treatment and prognoses were documented. Results: There were 7 male and 5 female patients in the series. The mean age was 37.92 ± 15.32 (19–62) years. There was history of upper respiratory tract infection in 7 patients, visual loss episodes in 3 patients, epileptic seizure in 2 patients, arthroplasty in 1 patient, cardiac arrhythmia in 1 patient, and COVID-19 (SARS-CoV-2) infection in 2 patients. Focal lesion was detected in the splenium of the corpus callosum with diffusion-weighted MRI which resolved with repeat diffusion MRI and clinical symptoms improved. Conclusions: Axial diffusion-weighted MRI images show typical splenium ovoid lesion of corpus callosum in patients with MERS. Patients with MERS have a good prognosis. It is important to consider MERS as one of the differential diagnoses in adult patients with fever and cognitive impairment.