Cognitive changes, depression, arthralgia and dermatitis developed in a 33-year-old woman 5 years after a jejunoileal shunt for massive obesity, The dermatitis and low serum carotene and vitamin C values suggested vitamin deficiencies, The serum magnesium concentration also was low. Vitamin and mineral replacement led to amelioration of the physical and psychological symptoms; the improvement has been maintained at 18-month follow-up. The favourable changes were documented with the Wechsler Adult Intelligence Scale, the Minnesota Multiphasic Personality Inventory and test performance ratings. It is concluded that the surgical procedure caused vitamin and magnesium deficiencies and that these resulted in the patient's symptoms.