If patients are discharged from the hospital prematurely, many may need to return within a short period of time. This paper investigates the relationship between length of stay and readmission within 30 days of discharge from an acute care hospitalization. It applies a two-part model to data on Medicare patients treated for heart attack in New York state hospitals during 2008 to obtain the expected cost of readmission associated with length of stay. The expected cost of a readmission is compared with the marginal cost of an additional day in the initial stay to examine the cost trade-off between an extra day of care and the expected cost of readmission. The cost of an additional day of stay was offset by expected cost savings from an avoided readmission in the range of 15% to 65%. Results have implications for payment reform based on bundled payment reimbursement mechanisms. Copyright © 2014 John Wiley & Sons, Ltd.