The results of autopsies performed in the pathological department of the Infectious Diseases Hospital named after. S.P. Botkin during the siege of Leningrad (from September 8, 1941 to January 27, 1944). The structure of diseases of the deceased varied during different periods of the siege of Leningrad. In the first period (September—December 1941), diphtheria, dysentery, measles, typhoid fever, and scarlet fever prevailed among the diseases. The most common causes of death in the second period (April—December 1942) were typhus, dysentery, tuberculosis, lobar pneumonia, and typhoid fever. Nosological structure in the third period of the blockade (January 1943 — January 1944): tuberculosis, dysentery, cachexia, lobar pneumonia, infectious jaundice. The discrepancy between clinical and morphological diagnoses is most often noted for the following nosology: pulmonary tuberculosis, typhoid fever, pneumonia, stomach and hepatopancreatobiliary cancer, measles, influenza. The first period of the blockade was distinguished by a high specific proportion of examination of children’s bodies — 51.2% of all autopsies; in subsequent periods, the specific share of autopsies of deceased adults (20—59 years) increased to 76.2%. The difference in the nosological structure and age groups of those who died during different periods of the siege of Leningrad was determined by the epidemiological situation in the city, social and living conditions and medical and organizational factors. Conducted in the pathological-anatomical department of the hospital named after. S.P. Botkin during the siege of Leningrad, pathological studies made it possible to timely establish the causes of deaths and identify the peculiarities of the course of infectious diseases against the background of cachexia. Regularly held clinical and anatomical conferences contributed to the reduction of defects in the diagnosis and treatment of infectious diseases.