Pain is more often lateralised on the left, except in the case of trigeminal neuralgia. The factors which promote lateralisation of pain are reviewed and it is noted that hysterical conversion symptoms are also more common on the left. Experimental evidence implies that the right hemisphere is less efficient than the left in processing cutaneous sensory input. Neurological and psychiatric data support the view that the right hemisphere is dominant for emotional experience and this may help to determine the left-sided preponderance of pain.