The current prospective study of 126 older adults examined the new problems and iatrogenic events developing in post-acute rehabilitation. Data were extracted from the electronic health record and a consensual agreement process was used for coding. Of the 578 new problems, 66% ( = 381) were not related to the primary problem treated at the hospital; 41.7% ( = 241) were iatrogenic adverse events. The median problem-free duration was 3 days and median duration to a moderate to severe problem was 8 days. Medication-related adverse events were common. This study did not show that comorbidity or functional level should be used in determining the likelihood of older adults developing new problems or iatrogenic events during post-acute rehabilitation. Inferential findings suggest older adults with a psychiatric diagnosis, cognitive impairment, or failure to thrive may require extra measures, such as comprehensive assessment and early intervention, to prevent new problems and iatrogenic events. [(6), 293-304.].