Pre-clinical studies have consistently found that most general anaesthetics produce accelerated apoptosis in the developing brain. The effect has been seen in species ranging from the nematode to the non-human primate. A variety of other effects are also seen. There is also some evidence that animals exposed to anaesthesia are at increased risk of deficits in memory and learning. The effects are only seen with prolonged exposure. There are numerous problems in translating these findings to human clinical scenarios. Several human cohort studies have found an association between surgery in infancy and increased risk of poorer neurobehavioural outcome; however the possibility of confounding factors such as co-morbidity and surgery itself make it impossible to determine if these associations are due to anaesthesia toxicity. A recent trial and cohort studies suggest that an exposure of less than an hour does not increase the risk of poor outcome.