Dental caries (decay) is a common disease in children. The consequences of dental caries include pain and infection and this has a major impact on children and their families. In severe cases children may require a general anaesthetic for removal of decayed teeth. Dental caries runs in families and about 50% of the risk of caries is due to genetic factors. Despite this, the individual genetic factors responsible are not well understood, probably because previous studies have been too small to find individual genetic factors. We have been asked to contribute data from ALSPAC to a new analysis, which will have a larger overall study size than previous analyses, and a greater chance of finding new genetic factors.