BACKGROUND: This study investigated the relationship between recent morphine use and risk of subdural haemorrhage (SDH) in patients with cancer. METHODS: This study identified a malignancy cohort of 25,322 patients who had never received morphine treatment. In this malignancy cohort, 200 patients who subsequently developed SDH were designated as the SDH group. Control-group patients without SDH were selected from the malignancy cohort and were matched ∼4:1 to each SDH case for age, sex, year of cancer diagnosis and index year. Morphine use was designated as 'recent' if the prescription duration covered the index date or ended within 6 months before the index date. Logistic regression was used to estimate odds ratios and 95% confidence intervals and a multivariable model was applied to control for age, sex and cerebrovascular disease. RESULTS: Compared with non-morphine users, patients with cancer who received morphine within 6 months of the index date exhibited a 2.58-fold (95% CI = 1.23-5.39) increase in the risk of developing SDH. The risk of SDH development increased as the duration of morphine treatment increased. CONCLUSION: The incidence of SDH in patients with cancer in Taiwan is associated with recent morphine treatment (≤6 months) and is dependent on the duration of morphine use.