Clinical-catamnestic examination of patients with oligophrenia (71 subjects) who performed socially dangerous acts and were brought to the Research Institute of General and Forensic Psychiatry named after V. P. Serbskiĭ for in-patient forensic psychiatric expertise was carried out. All the individuals examined are people who at least once were recognized irresponsible with diagnosis "oligophrenia at debility level". Presence of dynamic shifts both in main symptomatology of illness and in concomitant emotional-volitional manifestations were detected; prognostic variants of disease development and social adaptation of oligophrenics were noted. Group of patients with mental deficiency, who needs introduction of "limited sanity" term was singled out.