The principal clinical and pathological findings in 16 fatal cases of human African trypanosomiasis caused by T.b. Gambiense are described. The changes in the brain took the form of a non‐specific lymphoplasmacytic meningo‐encephalitis of varying intensity. Other features included morular cells, diffuse microglial hyperplasia, and large reactive astrocytes in the white matter. Carditis was identified in 10 cases. Acute reactive arsenical encephalopathy appeared to be the principal cause of death in 10 patients. Convulsions figured prominently in this type of encephalopathy in seven patients and were sufficiently severe to produce hypoxic brain damage. In three cases of acute reactive arsenical encephalopathy the structural changes in the brain were those of acute haemorrhagic leucoencephalopathy.