OBJECTIVE Detailed features of chronic subdural haematoma (cSDH) associated with disturbance of consciousness and acute-on-chronic subdural haematoma (a/cSDH), in which acute subdural haematoma overlaps cSDH, remain poorly understood. The object of this study was to clarify both characteristics of cSDH associated with disturbance of consciousness and the significance of a/cSDH. METHODS Clinical factors and computed tomography (CT) findings were retrospectively investigated in 349 consecutive patients admitted between 2006 and 2013 and diagnosed with cSDH. RESULTS Glasgow Coma Scale (GCS) was ≤ 8 in 21 patients (6.0%) and 9-14 in 29 patients excluding aphasia and/or dementia (8.3%). Multiple logistic regression analysis indicated that a/cSDH, female sex and haemodialysis were significantly related to severe disturbance of consciousness (GCS ≤ 8). Predictors for a/cSDH observed in 29 patients (8.3%) were trauma history within 7 days before admission, high prothrombin time-international rate, and use of anticoagulants and/or antiplatelets. Unfavourable outcomes were observed in 29 of 299 patients (9.7%) without consciousness disturbance, compared to 27 of 50 patients (54%) with consciousness disturbance. Predictors of unfavourable outcome were consciousness disturbance, increase in age, malignancy, trauma history within 7 days and haemodialysis. CONCLUSIONS Disturbance of consciousness associated with cSDH, often caused by either a/cSDH or concomitant disease, frequently resulted in unfavourable outcomes. As a result, in cSDH patients associated with disturbance of consciousness, underlying conditions, especially a/cSDH, which is often caused by haemostatic abnormality, should be clarified and managed.