Aims: To determine the prevalence of adverse drug event (ADE)‑related admissions and the related drugs. Setting and Designs: This study was conducted prospectively in two medical wards in Malaysia. Subjects and Methods: Information was collected from patients’ medical and medication charts over a period of 24 weeks. All screened patients were assessed using a list of criteria and were classified into: Therapeutic failure (TF), adverse drug reaction (ADR), medication error (ME), and drug overdose (DO). Patients admitted due to ADEs and its subcategories were analyzed and presented in counts and percentages. The prevalence of ADE‑related admissions and the drug associated with each category were identified and calculated. Results: Out of 1,200 screened patients, 39% (n = 443) were ADE‑related admissions. A total of 483 ADEs were identified; 79% (n = 351) were due to TF, 21% (n = 94) were due to ADR, 5% (n = 21) were due to DO, and 3% (n = 15) were due to ME. Cardiovascular drugs, antidiabetics, and antiasthmatics were most commonly associated with these admissions. The most common complaint by patients admitted due to a TF was chest pain, whilst hypoglycemia was the main cause of admission related to ADRs. Conclusions: The prevalence of admissions related to ADEs is high in Malaysia and this was mainly contributed by admissions related to TF. Some useful strategies such as educational interventions on the main causes of ADEs, monitoring of patients prescribed with drugs most commonly associated with ADEs, and appropriate prescribing should be targeted at all healthcare professionals to prevent future occurrences. However, further investigation is needed to clarify the high proportion of patients admitted due to TF.