Background: Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell disorders and the diagnosis of MDS is mainly based on morphological findings of peripheral blood and bone marrow. The present study was undertaken to study morphological changes in bone marrow on trephine biopsy in MDS and compare with age matched controls. Method: All trephine biopsies done over a six year period time 2013-2018 along with complete blood count, aspirate and cytogenetic report were studied in a Tertiary Care Hospital . 40 cases diagnosed as MDS were selected and in each case, detailed morphology of cellularity and all 3 cell lines was studied including distribution of cells. Cases were compared with 20 age matched controls, in whom bone marrow biopsy was done for cytopenias which were beyond doubt not cases of MDS. Results: We found on peripheral smear nucleated RBC (7 cases), macrocytes (12 cases), pseudo-pelger-huet anomaly in neutrophils (10 cases) and blasts (6 cases). On bone marrow biopsy, 39 out of 40 cases showed adequate smear. 23 cases showed increased cellularity (hypercellular). Monolobated megakaryocytes (20 cases) and micromegakaryocytes were found to be statistically significant findings. Myeioid series showed left shift in all cases. Erythroid series were hyperplastic and most cases (31 cases) showed megaloblastic and normoblastic marrow. 13 cases showed dyserythropoiesis, (p<0.01). On bone marrow aspiration, 20 cases showed hypercellularity, 14 showed micromegakaryocytes, 22 showed monolobated megakaryocytes, 19 showed hypogranular myeloid cells. Most cases (30; 75%) showed blasts <5%. 29 cases showed hyperplastic, megaloblastic and normoblastic erythroid series. Dyserythropoiesis was seen in 23 cases, (p<0.01). 24 (60%) cases were positive for cytogenetics and 10 cases on follow got transformed to acute leukaemia (AL). Conclusion: The conclusion is drawn that bone marrow aspirate and trephine biopsies are complementary procedures and both are required for diagnosis and also the cytogenetics remains the crux of diagnosis in MDS.