Background: In live-born children with Down syndrome it may be very difficult for the clinician or midwife assisting at the delivery to recognise Down syndrome in newborn babies due to varying physical appearances. Meanwhile more and more therapeutical interventions become available that should start early in life. We were interested in the age at the postnatal diagnosis of Down syndrome, and found no literature on the subject. Methods: We studied the age at the diagnosis of Down syndrome for live-born babies born in the period of 1981-2000 and registered by the European Registration of Congenital Anomalies in the northern part of The Netherlands. Results: For 289 children, data on the age at the postnatal diagnosis were available, in 70.8% of whom there was suspicion of DS on the day of birth. In 1.7% of the cases, the diagnosis was made after 1 year. Place of birth and the specialty of the health worker assisting at the delivery were associated with age at diagnosis. When the child was delivered at hospital, 96.4% of the Down syndrome cases had been diagnosed within 1 month compared to 81.3% following home delivery. Conclusion: In some cases of Down syndrome in liveborn babies, the diagnosis is made only after months or a year. The diagnosis was made faster in babies born in hospital compared to those born at home.