Health information technology (IT) adoption, it is argued, will dramatically improve patient care. We study the impact of hospital IT adoption on patient outcomes focusing on the role of patient and organizational heterogeneity. We link detailed hospital discharge data on all Medicare fee-for-service admissions from 2002-2007 to detailed hospital-level IT adoption information. For all IT-sensitive conditions, we find that health IT adoption reduces mortality for the most complex patients but does not affect outcomes for the median patient. Benefits from health IT are primarily experienced by patients whose diagnoses require cross-specialty care coordination and extensive clinical information management.