LVHN is warning patients their data could have been stolen in a hack earlier this year.
LVHN says a third-party service that transfers patient files got hacked in January.
Stolen information includes patient medical record numbers, diagnoses, and billing information, among other things.
LVHN says Guidehouse, which provides consulting services to the health network, didn't find out about the attack until March. It then notified LVHN about it in June.
Guidehouse has since stopped using the third-party service that had been compromised.
It's not clear how many patients were impacted.
The incident did not involve any unauthorized access to any systems or files maintained by the LVHN information technology systems, LVHN said.
"We regret that this incident occurred and take the security of personal information seriously," LVHN said in a statement.
Guidehouse says it doesn't know of any misuse of patient information but it has notified people who they had contact information for, and is offering them free identity protection and credit monitoring services for two years.