This case report describes carbon monoxide (CO) poisoning in a woman. CO is a toxic, odourless and colourless gas. Delayed cognitive sequelae have been described in up to 40% of patients with significant CO poisoning. A 77-year-old woman suffered from severe smoke- and CO poisoning and received hyperbaric O2 therapy, but she continued to have memory impairment and unsteady gait at day 26. Brain MRI showed diffuse white matter lesions in both hemispheres with increased signal on diffusion-weighted imaging. Diagnosis, pathogenesis and treatment of CO poisoning are discussed.