The Joint Commission has identified miscommunication as a leading cause of sentinel events, the most serious adverse events, but it is unclear what role miscommunications play in malpractice claims. We sought to determine the proportion of medical malpractice claims involving communication failure and describe their nature, including providers involved, locations, miscommunications types, costs, and the potential for handoff tools to avert risk and associated costs. We retrospectively reviewed a random sample of malpractice claims from 2001 to 2011, collected in CRICO Strategies' Comparative Benchmarking System, a national claims database. Two researchers reviewed cases to determine if a claim involved communication failure, its type, and potential preventability using a communication tool. Interrater reliability was assessed by dual review of 50 cases (81% agreement, κ = 0.62 for evidence of miscommunication). Claimant demographics, case characteristics, and financial data were analyzed. Communication failures were identified in 49% of claims. Claims with communication failures were significantly less likely to be dropped, denied, or dismissed than claims without (54% versus 67%, P = 0.015). Fifty-three percent of claims with communication failures involved provider-patient miscommunication, and 47% involved provider-provider miscommunication. The information types most frequently miscommunicated were contingency plans, diagnosis, and illness severity. Forty percent of communication failures involved a failed handoff; the majority could potentially have been averted by using a handoff tool (77%). Mean total costs for cases involving communication failures were higher ($237,600 versus $154,100, P = 0.005). Communication failures are a significant contributing cause of malpractice claims and impose a substantial financial burden on the healthcare system. Interventions to improve transmission of critical patient information have the potential to substantially reduce malpractice expenditures.