We reviewed the charts of 10 patients who were admitted to the Massachusetts Eye and Ear Infirmary over a 10-year period with the diagnosis of Bacillus species endophthalmitis. To our knowledge this is the largest single series in the literature and includes the first two reported cases of Bacillus endophthalmitis following glaucoma filtering procedures. Seven cases developed following penetrating ocular trauma. One occurred in an intravenous drug abuser. Five eyes ultimately underwent enucleation; only the two eyes that developed endophthalmitis after elective surgery retained useful vision. Review of the literature indicates that parenteral and intravitreal antibiotic prophylaxis against endophthalmitis after penetrating ocular trauma should include gentamicin, in combination with vancomycin or clindamycin, to provide adequate coverage against infection with Bacillus spp., as prognosis is poor once infection is established. Bacillus spp. cultured from ocular tissues or fluids should not be dismissed as contaminants.