There is considerable debate as to the appropriate role of helicopter transfer of sick patients. The debate over helicopter transfer of high-risk obstetric patients is even more intense. There is clear evidence that high-risk neonates are more likely to survive when they are delivered in a perinatal center compared with local delivery followed by transfer. On the other hand, there is concern that in-flight delivery entails "extreme risks, both to mother and child." In spite of this debate, there has been little research into the frequency of delivery during transport to a hospital or into the mortality associated with such a delivery. A study involving a single center suggests that the incidence of in-flight delivery is very low. We contacted all American Society of Hospital-Based Emergency Air Medical Services (ASHBEAMS) member air ambulance programs to determine the national statistics for in-flight delivery and associated perinatal mortality. We found no instances of in-flight delivery in 357 helicopter transports; 315 of these women were in active labor at the time of transport and 72 were in the accelerated phase of labor. There is evidence that these flights were screened for safety. Airplane flights generally took more time than helicopter flights (P less than .05), and there was one in-flight delivery during 88 airplane transfers. Also presented are additional data that suggest in utero transport of high-risk fetuses to a perinatal center by helicopter is cost effective.