Introduction: Thrombosis is the coagulation of blood in the vascular conduits. It is a significant cause of morbidity worldwide, decreased one year survival and increased mortality ratio among cancer patients. Despite this, identifying determinants of thrombosis in cancer patients is still not well addressed in our country. Objective: To identify determinants of thrombosis among cancer patients in the oncology unit at public specialized hospitals of Bahir Dar city, Northwest Ethiopia, 2022. Methods and materials: An unmatched case-control study was conducted from June to August 2022. About 98 cases and 294 controls were selected by consecutive and systematic random sampling. Data was collected and extracted through a structured interviewer-administered questionnaire and data extraction checklist by using epicollect5 mobile application. The data was entered in epi data 4.6 and exported into SPSSS 25. Multiple logistic regression analysis was performed to identify possible factors. Hosmer-lemeshow goodness of fit test was used to check the model. Finally, independent predictor variables of thrombosis were identified based on adjusted OR (AOR) with 95% CI and a p value of 0.05. The result was presented by a statement and tables. Results: The odds of thrombosis among cancer patients were 3.5-fold (AOR = 3.5, CI[1.56, 8.22]) higher in chronic medical illness, four-fold (AOR =4.04, CI[1.59, 10.22]) in cardiovascular diseases, 2.72-fold (AOR= 2.7[1.13, 6.53]) in renal diseases, 3.7-fold (AOR = 3.7, CI[1.5, 8.9]) in trauma (<1 month), 6.8-fold (AOR = 6.8, CI[2.16, 21.9]) and 15.4-fold (AOR = 15.4, CI[4.27, 55.9]) in high grade cancers(III and IV), 8.3-fold (AOR = 8.3, CI[3.5, 19.7]) in immobilization, 4.2- fold (AOR = 4.24, CI[1.97, 9.11] and 11.9-fold (AOR = 11.9, CI[2.59, 55.9]) in prolonged usage of chemotherapy(5-8 months and >9 months) and 14.2-fold (AOR = 14.2, CI[5.2, 38.9]) higher in cancer patients with history of recent surgery(<6 months). Conclusion and recommendation: This study revealed that chronic medical illness, cardiovascular diseases, renal diseases, trauma (<1 month), high-grade cancer (grade III and IV) immobilization, recent surgery (<6 months), and Dar city prolonged usage of chemotherapy (more than five months) were significantly associated with thrombosis. Therefore, health care professionals and concerned organizations better to work on factors of this study finding. Keywords: Thrombosis, Cancer patients, Determinant, oncology unit, Bahir TABLE OF CONTENTS DECLARATION SHEET iii ACKNOWLEDGMENTS v ABSTRACT vi LIST OF TABLES ix LIST OF FIGURES x ABBREVIATION AND ACRONYMS xi 1. INTRODUCTION 1 1.1. Background 1 1.2. Statement of the problem 3 1.3. Significance of the study 5 2. LITERATURE REVIEW 6 2.1. Determinants factors 6 2.1.1. Socio-Demographic factors 6 2.1.2. Cancer-related factors 7 2.1.3. Clinical and treatment-related factors 8 2.2. Conceptual framework 9 3. OBJECTIVE 10 4. METHODS AND MATERIALS 11 4.1. Study Area and Settings 11 4.2. Study Design and period 11 4.3. Population 11 4.3.1. Source population 11 4.3.2. Study population 12 4.3.3. Study unit 12 4.4. Eligibility criteria 12 4.4.1. Inclusion criteria 12 4.4.2. Exclusion criteria 12 4.5. Sample size determination 13 4.6. Sampling techniques and procedures 14 4.7. Study variables 15 4.7.1. Dependent variable 15 4.7.2. Independent variables 15 4.8. Operational definition 16 4.9. Data collection tools and procedures 17 4.10. Data quality assurance 17 4.11. Data processing and analysis 18 4.12. Ethical clearance 18 4.13. Dissemination of the result 19 5. RESULT 20 5.1 Socio-demographic characteristics 20 5.2 Patient clinical factors 22 5.3 Cancer-related factors 24 5.4 Treatment-related factors 26 5.5 Determinants of thrombosis among cancer patients 27 6. DISCUSSION 31 7. LIMITATION OF THE STUDY 34 8. CONCLUSION 35 9. RECOMMENDATION 36 REFERENCES 37 Annex 40 Annex I: Information sheet 40 Annex II: Informed Consent form 42 Annex III: Questionnaires 43