Grading and presence of myelofibrosis in bone marrow biopsies Myelofibrosis is seen as a primary disorder which is known as agnogenic myeloid metaplasia and is also associated with many malign and non-malignant diseases. Increased amount of myelofibrosis can cause bone marrow failure. Prompt diagnosis of disease which resulted with various degrees of myelofibrosis has a vita.l iınportance because of therapeutic and prognostic tüfferences. In this study, we investigated the frequency and degree of myelofibrosis and its relationship with number of megakaryocytes in 591 bone marrow biopsies which were repoırted in ur Department from 1987 to 1996. There were 40.27% myelofibrosis of all biopsies, respectively 19.96% were +, 10.99% were ++, 3.89% were +++, 5.41% displayed ++++ degree of myelofibrosis: The fiequency and degree of myelofibrosis had sigııificant difference among groups of diseases (p<0.0001). There was no correlation between number of megakaryocytes and degrees of myelofibrosis (p<0.05). Correlation between ages and myelofibrosis had no significant difference among the groups (p<0.05).