We examined six patients who presented with bilateral, progressive visual loss. Each patient had a bilateral decrease in visual acuity, poor color vision, and central or cecocentral scotomas. Optic nerve head appearance varied from normal to diffusely pale. All patients consumed tobacco, ethanol, or both. Each patient was folate deficient and had normal vitamin B12 levels. Patients were treated with oral folic acid, 1 mg per day. Visual acuity improved bilaterally in all patients (mean: five lines in 2 months). Folate deficiency should be considered in any patient with progressive bilateral optic neuropathy of unknown etiology. Treatment with folic acid can result in significant improvement in visual function.