Although the Centers for Medicare & Medicaid Services has focused on Medicare hospital readmissions for select diagnoses through the Hospital Readmissions Reduction program, there is no similar initiative for employers, who account for the majority of the 48% of private health care spending in the United States. Readmissions are costly and it is estimated that as many as half of these may be preventable. This study analyzes a national claims database to understand post-discharge transitions and their cost in the working population. Within an employer-sponsored, commercially-insured population, this study found that 4% of members are hospitalized annually and drive 37% of population health care cost. Of these members, 17% undergo additional admissions in the year following discharge and drive approximately 67% of the cost of the admitted population. This study found that the post-discharge site of care transitions has significant implications for the cumulative cost of care. More than a third of patients discharged home will transition to higher cost settings over the course of a year. Mental health and substance abuse diagnoses add significantly to admission/readmission rates and costs. Prior research indicates that post-discharge interventions that activate and engage patients in self-management are beneficial in mitigating overall cost and readmissions.