GABA B receptor antibody positive autoimmune encephalitis is rarely seen in clinical practice. It is usually associated with small cell lung carcinoma, and occasionally with neuroendocrine tumour (NET) of lung. GABA B receptor antibody can be associated with other autoimmune antibodies like antinuclear antibody and antibody to Glutamic acid decarboxylase. We present a case with GABA B receptor autoimmune encephalitis associated with neuroendocrine tumour of the duodenum with special emphasis on correlation between immunostaining of the tumour and presence of GABA B receptor antibody.