Among hospitalised patients, adverse drug reactions (ADRs) constitute a significant source of morbidity and death. ADRs in internal medicine units at a third-level university hospital were to be described in terms of their occurrence, severity, and cause in this study. Internal medicine units conducted a descriptive research using a structured approach, a review of clinical data, and interviews with hospitalised patients. To determine causation for patient adverse events, the Naranjo method was used. ADRs were also categorised using the Rawlins and Thompson standards. The research consisted of 15 case reports of patients, 6 males and 9 women. After applying the Naranjo algorithm to adverse events, 0 definite, 13 probable and 2 possible were identified ADRs. In the one case study we found ADRs as lethal to the patient. The frequency of ADRs was comparable to that which was noted in earlier studies conducted in internal medicine departments. To effectively detect and prevent ADRs, pharmacological surveillance activities in hospital wards must be systematised.