In a group of 65 twin pregnancies the difference of perinatal findings and antepartal test results was evaluated in relation to amnionicity and chorionicity. Monochorionic placentation was found in 33% of the pregnancies. The rate of foetal malformation (11%), neuromuscular dysfunction (6%), perinatal mortality (11%) and duration of neonatal intensive care was increased in those cases. The most useful diagnostic tool was B-Mode-ultrasound (first detection and surveillance of multiple pregnancy, especially diagnosis of inter-twin growth discordancy). Non stress test and Doppler sonography were found to be of value as additional tests for detection of functional differences between both twins. There were no differences between findings in first and second twin as well as between findings in pregnancies with mono- or dichorionic placentation.