The case of a patient with progressive systemic sclerosis, who developed hypoglycaemia and insulin autoantibodies, is described. Repeated blood glucose measurements showed levels < 2.8 mmol/l. High immunoreactive insulin levels, with undetectable free insulin, led to the discovery of anti-insulin antibodies in the patient’s serum. He had no history of exogenous insulin use and was receiving penicillamine treatment. A double mechanism for the autoimmune insulin syndrome in this case is proposed: acting in a patient with increased humoral immunoresponsiveness, penicillamine might have induced the development of insulin autoantibodies.