X-linked adreno-leukodystrophy and its adult variant, adrenomyeloneuropathy, are caused by mutations in ABCD1 that encodes a peroxisomal membrane protein of unknown physiological significance. In spite of identical mutations, they can have markedly divergent neurological and neuropathologic characteristics. Adreno-leukodystrophy classically presents in normal boys with mild neuropsychiatric features, which progress to frank neurological signs, the vegetative state and death in approximately three years. Adrenomyeloneuropathy typically affects young men with spastic paraparesis and sensory ataxia that can progress over decades. The neuropathologic correlate for adreno-leukodystrophy is severe inflammatory demyelination of posterior cerebral white matter, while a chronic distal axonopathy of spinal cord and peripheral nerve occurs in adrenomyeloneuropathy. Consequently, both modifier genes and environmental factors have been implicated in their pathogeneses. We report five cases of adreno-leukodystrophy whose onsets were initiated by moderate to severe head trauma, two of whom were conversions from adrenomyeloneuropathy. Their clinical courses were rapidly incapacitating, short (i.e., weeks to a few years) and fatal due to marked cerebral inflammatory demyelination. These cases, in concert with several previous reports, indicate that head trauma is one environmental factor that can have a profoundly deleterious effect on those genetically at risk for, or with milder clinical phenotypes of, this disease. Avoidance of potential head trauma and a rapid response to episodes of moderate to severe head trauma in this patient population seem prudent.