During the past four years, an attempt has been made in Malmö to reduce the frequency of preterm termination of twin pregnancies. For this purpose, the entire pregnant population of this medium-sized city was subjected to general ultrasonic screening in the second trimester. This detected 88 per cent of the twin pregnancies. The screening has a methodological error of 2 per cent. Eightysix of the women with twin pregnancy were subjected to bedrest in hospital for more than two weeks in the second half of gestation. The incidences of twins born with birth weight below 1 500 g and of twins light-for-gestational-age were reduced compared with those a decade earlier. Also the group of twins born before the 37th week decreased, and the perinatal mortality rate fell to the same level as in singleton pregnancies. Early detection of twin pregnancies followed by rest for the pregnant women seems to contribute to an improved outcome of these gestations.