Aim: To identify older patients’ risk factors for drug-related readmissions and assess the preventability of older patients’ drug-related revisits. Methods: Post-hoc analysis of a randomised clinical trial with patients aged ≥ 65 years at eight wards within four hospitals in Sweden. The primary outcome used to identify risk factors was drug-related readmission within 12 months post-discharge. A Cox proportional hazards model was made with sociodemographic and clinical baseline characteristics. Four hundred trial participants were randomly selected and their revisits (admissions and emergency department visits) were assessed to identify potentially preventable drug-related revisits, related diseases and causes. Results: Among 2,637 patients (median age (interquartile range) 81 (74–87) years), 582 (22%) experienced a drug-related readmission within 12 months. Sixteen risk factors (hazard ratio > 1, p < 0.05) related to age, previous hospital visits, medication use, multimorbidity and cardiovascular, liver, lung and peptic ulcer disease were identified. The 400 patients experienced a total of 522 hospital revisits, of which 85 (16%) were potentially preventable drug-related revisits. The two most prevalent diseases and causes related to preventable revisits were heart failure (n=24, 28%) and chronic obstructive pulmonary disease (n=13, 15%), and inadequate treatment (n=23, 27%) and insufficient or no follow-up (n=22, 26%). Conclusion: Risk factors for drug-related readmissions in older hospitalised patients were age, previous hospital visits, medication use and multiple diseases. Potentially preventable drug-related hospital revisits are common and might be prevented through adequate medication use and follow-up in older patients with cardiovascular or lung disease.