To assist clinicians in the diagnosis and management of ocular siderosis. The diagnosis and management of three cases of ocular siderosis secondary to a retained iron-containing intraocular foreign body are described. Noteworthy features included: 1) the characteristic features of a tonic or Adies pupil (one case) and 2) the failure of high-resolution computed tomography scanning and plain film radiography to detect the intraocular foreign body (two of three cases). In contrast, ultrasonography demonstrated the intraocular foreign bodies in all cases and accurately localized them to the inferior retinal quadrants. A third noteworthy finding was that a preoperative electroretinogram reduction in amplitudes of as much as 40% compared with that of the uninvolved eye was compatible with excellent vision, and that the electroretinogram returned to normal after the intraocular foreign body was removed. Ocular siderosis should be considered in the differential diagnosis of a tonic or Adies pupil. To detect an occult intraocular foreign body, clinicians should not rely exclusively on computed tomography scanning or plain film radiography, but should also use B-mode echography with careful study of the inferior quadrants. In ocular siderosis a preoperative electroretinogram reduction in amplitudes of as much as 40% may be reversible after intraocular foreign body removal.