Three girls showed psychomotor regression arising between the 1st and 2nd year of life, after an initially normal development. Language, gait, chewing and swallowing were especially affected, whereas elementary sensory and motor functions were relatively spared. All displayed a particular disorder of breathing, which was irregular and inadequate during wakefulness, returning to normal during sleep. There are similarities between these patients and the syndrome of cerebral atrophy with hyperammonaemia, even though brain CT and biochemical studies, including ammonaemia, were all normal.