Language disorders are criteria of psychopathology diagnostics listed both in the 10th revision of International Statistical Classification of Diseases and Related Health Problems (ICD-10) and the Diagnostic and Statistic Manual of Mental Disorders (DSM). However, structure and grammar remain understudied in this aspect, which makes structural analysis a relevant research topic. A structural analysis of written narrative may objectivize particular language disorders, thus facilitating psychodiagnostics of different mental disorders. The research objective was to describe the structural features of written narratives obtained from 127 patients with schizophrenic, bipolar, and personality disorders. The narratives were subjected to structural and statistical analyses. Schizophrenic narratives demonstrated a poor vocabulary, a low volume, and a high degree of formality with a passive narrator. Bipolar texts tended to be long, detailed, egocentric, and active, with multiple participles. Patients with personality disorders emotionally relived their memories, producing reflective written narratives with a lot of actors. The final list of written speech indicators to be used to distinguish between schizophrenic, bipolar, and personality disorders included such variables as text volume, verb tense, non-finite verb forms, first-person singular pronoun, number of actors, passive / active narrator, and laconic / detailed narration.