The term ‘Myelofibrosis’ is used to describe any increase in bone marrow stromal fibers. There are several conditions, both neoplastic and non- neoplastic. There are 2 types of fibers which are deposited in the marrow. 1) Reticulin fibers 2) Collagen fibers Increased reticulin is associated with many benign and malignant conditions while increased collagen fibrosis is particularly prominent in late stages of myeloproliferative neoplasia or following tumor metastasis to the bone marrow. Objectives: To look for the etiology of myelofibrosis, correlating the clinical features with morphology and to classify the grade of reticulin fibrosis (grade 2 or 3) and look for collagen fibrosis and look for bone changes of osteosclerosis. Materials and Methods study design: Combined retrospective & prospective observational study. Period: January 2018-June 2020 (over a 2½ year period). Study area: Department of Pathology (hematology laboratory), NIMS, Hyderabad, India. Sample size: The study included 300 cases of myelofibrosis of varied aetiologias. The cases were retrieved from the Hematopathology records at a tertiary care center. The clinical details, including all investigations, were obtained from the patient’s medical records. Inclusion criteria: All cases where the bone marrow biopsies with diffuse, ≥ 2 Grade reticulin condensation, were included in the study. Exclusion criteria: Cases where peripheral smear/marrow cytology/trephine biopsy not available for review. Cases with incomplete clinical details. Statistical analysis: Statistical analysis was done using Fisher’s exact test and p value ≤0.05 is considered statistically significant. Results: Age range from19 to 90 years with mean of 45. Ther male preponderance ratio of 1.2:1.The cases were classified into broad categories as myeloproliferative neoplasms 90(30%)cases, acute Leukemia in 71(23%), reactive fibrosis in 60 cases (20%), lymph proliferative disorders in 9%) plasma cell neoplasm 7% cases, MDS in 14 (4.6%), metastases-9 cases (3%), granulomatous inflammation 5 cases (1.6%), auto- immune myelofibrosis (AIMF)in 3 cases (1%). Conclusion: The study included 300 cases with grade 2 or 3 reticulin fibrosis within trephine sections Even though diffuse reticulin fibrosis can be seen in nonneoplastic conditions, it is more commonly associated with clonally or neoplastic pathologies. Acute leukemia, MDS, lymphoproliferative disorders and plasma cell neoplasms can also be associated with reticulin fibrosis. Recognition and diagnosis of AIMF is important as it is a rare condition.