Ascension Health: 437,329 individuals, Apr 2025.

OCR classifies the incident as a hacking or IT incident, with the breached information held in a network server. Hacking/IT Incident is the type recorded on 100 of the 164 Missouri filings (61%) and on 81% of all filings submitted in 2025. Network Server appears on 38% of Missouri filings.

No business associate is recorded on the filing; 23% of Missouri filings do involve one. At 437,329 individuals the breach is 91 times the Missouri median filing of 4,800 and 109 times the national median of 4,000 across all 7,884 filings. It is one of 801 filings of 100,000 or more individuals.

As of 28 August 2026 the case is listed by HHS OCR under Cases Currently Under Investigation. OCR has not published a closing summary, so this page is limited to the fields on the filing itself; the archive entry that follows a closed investigation usually adds a short account of what was exposed and what the entity did afterwards.

Missouri's breach notification statute (Mo. Rev. Stat. 407.1500) requires notice to affected residents without unreasonable delay. Its attorney general threshold: more than 1,000 Missouri consumers. The HIPAA Breach Notification Rule ran alongside it: notice to affected individuals and to HHS without unreasonable delay and no later than 60 days after discovery, which is the clock that put this filing on the portal.

Multiplying 437,329 individuals by IBM's $160 customer-PII cost per record (Cost of a Data Breach 2025, the figure the site's calculator uses) gives a modelled $70.0M; the 2026 edition's $192 gives $84.0M. Both are modelled estimates with the method shown, not costs disclosed by Ascension Health. Because the filing is above the roughly 100,000-record range in which the per-record figure is reliable, the result is an upper bound, not an estimate: fixed costs are spread across far more records at this scale.