Accurate medication histories at hospital admission are an important element of medication safety. Discrepancies may have clinically significant consequences, especially in the elderly population. To assess the clinical pharmacist's performance in obtaining patients' medication histories and in reconciling these data with the medical records and medication orders and whether the patients' residential situation prior to hospitalization influences the number of drug discrepancies. A prospective observational study was conducted at a 29-bed acute geriatric ward of a Belgian university hospital. Medication histories acquired by clinical pharmacists were compared with those documented in the medical records by the attending physicians. All discrepancies were identified and categorized by an independent pharmacist and were scored for their clinical relevance in consensus by a senior internist and a senior geriatrician. Of the 215 screened geriatric (aged ≥65 years) patients admitted between October 27, 2007, and September 23, 2008, 197 were enrolled in the study. For patients living in the community, as well as those residing in a nursing home prior to hospitalization, clinical pharmacists identified significantly more preadmission drugs compared with physicians, with a median number of 8 correctly identified medications versus 6, respectively (p < 0.001). Extra identified drugs consisted of over-the-counter as well as prescription medications. Furthermore, 117 other medication discrepancies were noted, mainly related to erroneous drug identification and incorrect drug dose. In all, the clinical pharmacists identified 379 (24.2%) medication discrepancies, of which 188 (49.6%) were judged clinically relevant. Pharmacist-acquired medication histories enhance the medication reconciliation process, both in patients residing at home and in a nursing home prior to hospitalization. A focus should be placed on seamless care procedures that facilitate the transfer of medication histories between primary and secondary care in both of these populations.