Hypodontia, the absence of six teeth or less, is the most prevalent dentofacial malformation. The prevalence varies within populations, sex, dentitions and tooth-type. The prevalence in Europe is approximately 5%. Excluding third molars, mandibular second premolars and maxillary lateral incisors are most likely to be absent, with a prevalence of 2.5-4% and 2% respectively. The aetiology of hypodontia is multifactorial. Genetic syndromes found to be associated with hypodontia include ectodermal dysplasia, Down’s syndrome and cleft lip/palate. Examples of environmental factors are early childhood trauma to the alveolar process, and chemotherapy and radiotherapy in infancy. Intrauterine exposure of toxins, such as thalidomide, and maternal infections, rubella. Currently, there is limited research on maternal smoking, alcohol and caffeine consumption during pregnancy and its effect on hypodontia. The only study to investigate this was a case-control study in New Zealand with 89 patients. It found strong evidence that consumption of 10 or more cigarettes per day during pregnancy was associated with greater odds of the child having hypodontia (adjusted OR, 4.18; 95% CI, 1.48-11.8; P=0.007) . The conclusion from the paper is vague regarding mechanisms but suggests that oxidative stress from smoking affects foetal neural crest cells, which could explain the causal relationship between smoking and hypodontia. This interesting finding requires replication with a larger sample size, ideally using methods to pinpoint specific intrauterine effects. ALSPAC provides an opportunity to replicate this and use paternal smoking, alcohol and caffeine consumption as negative controls for the causal relationship between hypodontia and maternal smoking during pregnancy.