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The proven efficacy and safety of medical ozone therapy remains controversial [1–6]. In rats, ozone inhalation was shown to promote neuronal activation in stress-responsive regions of the central nervous system (CNS) [7], electrical activity alterations and changes in brain major neurotransmitter systems [8, 9]. We here describe two patients who developed cortical blindness and seizures shortly after intraarticular ozone infiltrations. There is only a prior report of top of the basilar stroke and Anton syndrome following ozone therapy [10]. A 75-year-old man complained of dizziness, slurred speech, tingling in the left extremities and visual loss, which developed 10 min after receiving a paravertebral ozone therapy session and autohemotherapy for spondylarthrosis. On admission he was fully aware with left neglect, cortical blindness, left central facial paralysis, and numbness and mild weakness of the left extremities. A brain magnetic resonance imaging (MRI) scan showed subcortical/juxtacortical white matter chronic ischemic lesions in the right cerebral hemisphere without evidence of acute lesions (Fig. 1a). Stenosis of the distal branch of the left cerebral posterior artery and a severe stenosis of the right carotid artery on MR angiograms were found. An EEG showed an alpha rhythm (8 Hz) predominantly in the left posterior region and a slow attenuated delta rhythm in the right hemisphere. A Tc-ECD brain SPECT showed bilateral hypoperfusion areas particularly in the left occipitotemporal region (Fig. 2). Twenty-four hours later, the patient presented visual hallucinations, various episodes of forced oculocephalic deviation to the left, clonus on left extremities and a tonic–clonic seizure. He was successfully treated with valproic acid and levetiracetam. A brain MRI performed 7 days later showed one small juxtacortical subacute ischemic lesion in the right occipital lobe (Fig. 1b). A 60-year-old woman presented with posterior cortical blindness and history of a tonic–clonic seizure, which developed shortly after intraarticular infiltration of ozone and procaine for the treatment of a left shoulder joint disease. On admission she was disoriented with repetitive speech, anterograde memory impairment and cortical blindness. The brain MRI showed a right acute ischemic cerebellar lesion (Fig. 1c). The EEG showed slowed brain D. V. Rolan (&) J. L. B. Cunat J. V. Hervas D. Escudero Neuroscience Department, Hospital Universitari Germans Trias i Pujol, Universitat Autonoma de Barcelona, Carretera de Canyet s/n, 080916 Badalona, Barcelona, Spain e-mail: doloviro@hotmail.com