Background: Chronic subdural haematoma (CSDH) is common of all intracranial haemorrhages specially in old age. Mortality is still 13% after invention of simplest and latest technique including operation. Incidence of CSDHs in over 65 years is 58.1 per 100,000 per year but only 3.4 per 100,000 per year in those under 65 years of age. So, age has a great role inducing CSDH, there is also chance of intracranial haemorrhage on anti-platelet & anticoagulant drugs, platelet & coagulation dysfunction. Major trauma to head produces acute haematoma but minor trauma should take into cognizance for CSDH. The purpose of this study was to take details history, analysis of patients to find out aetiological factors of chronic subdural haematoma and to take precautions regarding them specially most one to avoid preventable morbidity and mortality. Materials and Method: This prospective study was carried out in Combined Military Hospital (CMH), Dhaka from March 2018 to March 2019. All of our patients above 20 years of age; were admitted and diagnosed clinically and confirmed by CT scan head as CSDHs. Total number of patients were 50; randomly allocated and sampling was done as per inclusion and exclusion criteria. Elaboration of details history, through examination including neurological examination, meticulous investigations including CT scan of head was done. Statistical analyses were performed by using the Statistical Package for Social Sciences version 26 for Windows (SPSS). Results: In our study 50 cases were finally selected as CSDHs and diagnosed clinically then confirmed radiologically. The most of the patients 39 (78%), 51-80 years age group, male were 41(82%) and female were 9(18%) in number. In this study, it was observed that unknown aetiology 7(14%), on anti-platelet drug 10(20%), on anti-coagulant drug 6(12%) and 27(54%) subjects had trivial head trauma. Explored aetiology; trivial head trauma, on anti-coagulant and anti-platelet medication were 43(86%) in number. Conclusion: Diagnosis of CSDH is relatively easier than to find out aetilogy. We should cautious about the causative factors specially most common like trivial head trauma in old age & keen observe them and avoid coagulopathic medication if not essential.