Potentially inappropriate medications (PIM) and potential prescribing omissions (PPO) in older adults are associated with adverse events, increased hospital readmissions, and lower health-related quality of life. This study aimed to estimate the prevalence of PIM and PPO at hospital admission and discharge and to explore the impact of clinical pharmacist involvement. Patients in the intervention group (with pharmacist involvement) had lower rates of PIM at discharge compared to the group receiving usual care (no pharmacist involvement). There was no difference in PPO between groups. Patients admitted from nursing homes and other institutional settings were at increased risk of PIM at discharge.