Gastroschisis is the evisceration of the fetal intestine through a defect in the paraumbilical anterior abdominal wall with herniation of gastrointestinal structures into the amniotic cavity. Babies born with this condition are more likely to be born prematurely and to have had poor fetal growth. The anomaly requires immediate postnatal surgery, which has a good outcome in more than 90% of cases.1 It is a distressing condition for parents, however, and often requires a prolonged stay in a paediatric unit. Ten years ago our group reported in the BMJ that the national system for notifying congenital malformations (collated by the Office for Population and Census Surveys, now called the Office for National Statistics, ONS) showed an increasing trend in the number of babies born with gastroschisis in England and Wales between 1987 and 1993.2 No such marked increase was apparent for other congenital anomalies such as exomphalos. Gastroschisis was associated with a lower overall maternal age: the incidence among mothers aged under 20 is 4.71 per 10 000 total births compared with 0.26 per 10 000 total births to mothers aged 30-34. Furthermore, the incidence of gastroschisis was markedly higher in the northern regions of the United Kingdom (1.55 per 10 000 total births) than in the southeast (0.72 per 10 000 total births).2 The notification system is voluntary, however, and under-notification and misclassification of malformations may therefore be considerable, leading to under-ascertainment.3 This also favours over-notification of very visible anomalies such as gastroschisis while probably grossly underestimating non-visible lesions, such as heart defects. Nevertheless, even gastroschisis seems to be underestimated in ONS statistics.4,5 In contrast, regional registers for congenital anomalies aim to include all data from abortions, fetal loss, and infant deaths, as well as cross referenced information from paediatric surgical units. Such data sources have consistently shown better and more complete registration of congenital anomalies and have confirmed both an increasing incidence of gastroschisis among babies of teenage mothers and an overall increase year on year.6 This discrepancy between different register types has been well described.7 The UK's chief medical officer has expressed concern about the rising incidence of gastroschisis (L Donaldson, personal communication, July 2005) and has highlighted the importance to public health of rigorously compiled and centrally funded regional registers in providing information on congenital anomalies.8​8 Figure 1 Number of reported cases of gastroschisis between 1994 and 2004. Reproduced with permission from the Department of Health Recent data from the British Isles Network of Congenital Anomaly Registers (BINOCAR) confirm the increasing incidence of gastroschisis—from 2.5 per 10 000 total births in 1994 to 4.4 per 10 000 in 2004.8,9 Among babies of women aged under 20 the incidence of gastroschisis increased from 8.9 to 24.4 per 10 000 total births. In addition, the incidence in some registers is four times as high as in others across different regional registers—for example, the Welsh register indicates an incidence of gastroschisis of 6.2 per 10 000 total births, whereas the rate in North West Thames was 1.6 per 10 000. The observed increasing incidence of gastroschisis over time seems to be associated consistently with lower maternal age.2 Gastroschisis probably does not have a genetic cause because it occurs sporadically, with a relatively low recurrence rate. The most likely cause is early interruption of the fetal omphalo-mesenteric arterial blood supply. This may be associated with periconceptional tobacco smoking and use of recreational drugs such as alcohol, marijuana, and cocaine.10,11 The evidence for these associations is, however, only tentative and needs confirmation by carefully controlled cohort or case-control studies.12,13 Along with data from regional registers, such studies may lead the way to understanding the pathogenesis of this distressing condition and thus preventing it.