Bacillus cereus typically causes a self-limited foodborne gastrointestinal (GI) illness. Severe invasive infection occurs rarely, mainly among immunocompromised hosts. We describe a cluster of B. cereus infections among 5 patients with acute myeloid leukemia and chemotherapy-induced neutropenia. The initial case presented with occipital lobe abscess and was found on biopsy to have organisms consistent with Bacillus species. Within 1 week, a second patient died of fulminant brain swelling and hemorrhage. Neuropathologic autopsy and culture revealed B. cereus; hospital infection control and public health officials were notified. Three more patients died within the subsequent 9 months (2 patients had rapid massive hemorrhage and many bacilli reminiscent of Bacillus anthracis infection, and 1 patient had sparse bacilli, petechial hemorrhages, and border zone infarcts). Blood cultures yielded positive results in 3 of 5 cases. A possible route of infection was hematogenous dissemination via GI mucosal breaches (GI symptoms occurred in 3 of 5 cases, and postmortem GI ulceration was found in 3 of 4 cases). Bacilli were seen in 2 of 3 GI ulcerations. Epidemiologic work-up, including a site visit conducted by the Centers for Disease Control and Prevention, did not identify a clear common source but suggested the possibility of bananas as a food source. Bacillus cereus causes a rapidly progressive, hemorrhagic meningoencephalitis with high mortality among patients with neutropenia. Neuropathologists can play a key role in the detection of outbreaks.