Vitamin B12 deficiency causes a wide range of haematological, gastrointestinal, psychiatric and neurological disorders.Subacute combined degeneration (SCD) is a rare clinical manifestation characterised by dysesthesia, disturbance of position sense and spastic paraparesis due to the invovement of dorsal and lateral spinal columns. We report a case with SCD due to Vit B12 deficiency who recovered with replacement therapy but relapsed with a more severe clinical picture soon after he gave up the treatment. A 62 year old male admitted to the outpatient clinic with the complaint of difficulty in walking. He had position and vibration loss in all extremities which was more prominant in the legs. Bilateral lower extremity weakness with spastisity and hyperactive deep tendon reflexes were detected. Past medical history revealed hospitalization and treatment in the neurology clinic for Vit B12 deficiency. He had primarily sensory symptoms at the time of hospitalization which improved with the B12 replacement treatment. He presented with severe walking disability and spastic paraplegia weeks after the discontinuation of treatment. Moderate improvement was achieved with inpatient rehabilitation programme and he is now walking with the aid of a walker. He is on monthly intramuscular vit B12 injection therapy. SCD is a disabling neurological complication of Vit B12 deficiency. Early diagnosis and treatment play an important role in the reversibility of neurological deficits. Adherence to lifelong treatment is as important as early diagnosis in the prevention of inirreversible neurological impairment.