Ten Japanese boys with childhood adrenoleukodystrophy (ALD), one adult patient with adrenomyeloneuropathy (AMN), and two presymptomatic ALD boys were treated with dietary erucic acid (C22:1) for more than 12 months; except in a case of childhood ALD patient who died 7 months after beginning erucic acid therapy. During erucic acid therapy, the serum levels of very long-chain fatty acid (VLCFA) (C24:0/C22:0) decreased within 1-2 months in all patients, and these levels in four of the patients decreased to the normal range. Neurological examination and MRI findings in all 10 of the childhood ALD patients showed progression of the disease while they were receiving the dietary therapy. However, the mean interval between the onset of awkward gait and a vegetative state in diet-treated patients was significantly longer than that in the untreated patients. One AMN patient showed slight improvement of spastic gait and lessened pain in the lower limbs due to spasticity. The two presymptomatic ALD boys remained intact on clinical examination and on MRI findings for 38 and 23 months, respectively, after starting the diet.