The pancytopenia can be associated with intra and extra medullary disorders. When the etiology is not obvious, the examination of bone marrow is necessary. The study aims to report and discuss quantitative amendments in bone marrow and their causes in dogs with pancytopenia. Bone marrow aspirate was obtained from 65 dogs with pancytopenia over a period of 13 consecutive months for preparation of smears stained by Giemsa and observed in light microscopy. Five hundred cells differential count was held; and assessed myeloid:erythroid ratio, cellularity, megakaryocytes and direct parasitological examination. The data were evaluated by the Chi-square statistical test. Blood tests of 3120 canines with several clinical changes were analyzed to identify pancytopenia, which accounted for 167 (5.4%) dogs. Interpretation of quantitative characteristics was carried out from the bone marrow smear in 65 pancytopenic dogs and the etiology was established in 40 (61.5%) of these, which included infection by E. canis and L. chagasi, idiopathic aplastic anemia, chronic renal failure and co-infections. In 17 (26.2%) animals were not observed medullary changes. The most bone marrow change was observed myeloid and erythroid hypoplasia in 17 (26.2%) dogs, followed by myeloid and erythroid hyperplasia (24.6%). The myelogram association to the blood cell count allowed the identification of medullary findings and its participation on the occurrence of pancytopenia cases. The number of cases resulting from infectious diseases was 38 (58.5%) in canine assessed: significant number due to its endemic characteristic of the study region. Key words: Cytology. Canine. Cytopenia. Hemoparasites. Myelogram. ResumoA pancitopenia pode estar associada a distúrbios intra e extra medulares. Quando a etiologia não é óbvia, o exame da medula óssea é necessário. Este estudo tem como objetivo relatar e discutir alterações quantitativas na medula óssea e suas causas em cães com pancitopenia. De 65 cães pancitopêncicos atendidos durante um período de 13 meses consecutivos, foram realizados aspirados de medula óssea, corados com Giemsa, e observados em microscopia de luz. Quinhentas células foram observadas para contagem diferencial, razão mieloide: eritróide, celularidade, megacariócitos e exame parasitológico direto. Os dados foram avaliados pelo teste estatístico Qui-quadrado. Hemograma de 3120 caninos com diversas alterações clínicas foram analisadas para identificar a pancitopenia, encontrada em 167 (5,4%) cães. A interpretação das características quantitativas foi realizada a partir do esfregaço de medula óssea em 65 cães pancitotopênicos e a etiologia foi estabelecida em 40 (61,5%), incluindo infecção por