X-linked adrenoleukodystrophy (XALD) typically presents as a childhood cerebral demyelinating form, as an adult-onset adrenomyeloneuropathy or as adrenocortical insufficiency. Cerebral demyelination presenting in adolescence is unusual. We present an 17-year-old boy with adolescent-onset XALD initially manifesting with slowly progressive psychiatric symptoms. He was initially diagnosed with attention-deficit hyperactivity disorder and an acute psychosis. However, he was ultimately diagnosed with XALD based on his clinical course, neuroimaging findings and biochemical abnormalities. This case reiterates the atypical presentations of adolescent-onset cerebral XALD that may go unrecognised and misdiagnosed as a neurodevelopmental or psychiatric disease. Treatments for cerebral ALD are potentially life-saving, particularly when given early in the disease course.