Admission Medication Reconciliation (Med Rec) is an organizational practice designed to ensure patients' pre-admission medications are ordered correctly upon hospital admission. We describe the implementation of admission Med Rec at two academic health sciences centres, each having designed distinctly different processes. Common challenges encountered included the multi-step, inter-professional nature of Med Rec, staffing resource and workload concerns and frequent medical staff turnover in a teaching environment. Both teams found that participation in a national safety collaborative enabled the pilot initially; however, they later found the outcome measures suggested by the collaborative less useful and switched to internal compliance measures for establishing maintenance and spread. Common themes were identified among the critical success factors, with unique variations at each centre. Both teams acknowledged accreditation standards to be a major accelerator of implementation and spread. Using different measures of implementation success at each centre, the majority of patient admissions on the pilot units are complying with admission Med Rec. However, very high levels of compliance remain elusive. At Sunnybrook Health Sciences Centre's pilot unit, 62-77% of patients are being screened by a pharmacist and 65-75% of high-risk patients identified are undergoing Med Rec by a pharmacist. At The Hospital for Sick Children's pilot unit, 72-88% of patients have a physician's primary medication history documented on a Med Rec form and 57-73% of patients are also undergoing Med Rec by a nurse or pharmacist.