Introduction: Cognitive impairment, usually associated with seizures and psychosis, is one of the main symptoms of autoimmune encephalitis. The objective of our study is to analyse cognitive impairment in patients with autoimmune encephalitis. Methods: We conducted a descriptive cross-sectional study of clinical data from 39 patients older than 18 years diagnosed with autoimmune encephalitis. Twenty-two patients underwent neuropsychological assessment. Results: All but one of the patients presented cognitive impairment. Memory was the most frequently affected domain (90.91%), followed by language (50%), attention (45.45%), executive function (40.91%), praxis (40.91%), and visuospatial skills (9.09%). No association was found with disease progression time, age, sex, or education level. Results from cerebrospinal fluid analysis, electroencephalography, and brain magnetic resonance imaging studies revealed alterations in 77.27%, 57.89%, and 55% of cases, respectively. Conclusions: Memory is the most frequently affected cognitive domain; however, other cognitive domains were also altered in our patients. Neuropsychological assessment is crucial to determine which cognitive domains are impaired in patients with autoimmune encephalitis.