This study examines the association between the quality of hospital discharge planning and all-cause 30-day readmissions and same-hospital readmissions. The sample included adults aged 18 years and older hospitalized in 16 states in 2010 or 2011 for acute myocardial infarction, heart failure, pneumonia, or total hip or joint arthroplasty. Data from the Hospital Consumer Assessment of Healthcare Providers and Systems measured discharge-planning quality at the hospital level. A generalized linear mixed model was used to estimate the contribution of patient and hospital characteristics to 30-day all-cause and same-hospital readmissions. Discharge-planning quality was associated with (a) lower rates of 30-day hospital readmissions and (b) higher rates of same-hospital readmissions for heart failure, pneumonia, and total hip or joint replacement. These results suggest that by improving inpatient discharge planning, hospitals may be able to influence their 30-day readmissions and increase the likelihood that readmissions will be to the same hospital.