Maternity unit closures in France have increased distances that women travel to deliver in hospital. We studied how the supply of maternity units influences the rate of out-of-hospital births using birth certificate data. In 2005-6, 4.3 per 1000 births were out-of-hospital. Rates were more than double for women living 30km or more from their nearest unit and were even higher for women of high parity. These associations persisted in multilevel analyses adjusting for other maternal characteristics. Long distances to maternity units should be a concern to health planners because of the maternal and infant health risks.