Five patients (aged 19-52 years) were treated for a midbrain syndrome due to acute carbon monoxide poisoning and had clinical follow-up investigations for up to 18 months. Three patients recovered with minor neurological and neuro-psychological deficits and resumed their premorbid life-style. One patient had normal findings, while the fifth remained in a permanent vegetative state. Initial CT of the brain may fail to detect low-density lesions in the globus pallidus. If present, these lesions may either have disappeared, diminished, or remained unchanged at follow-up. Long-term outcome seems to show a closer link to white matter changes, which are at present best investigated by magnetic resonance imaging. The additional value of determining visual evoked responses at repeated follow-up is suggested by the present investigation.