The transvaginal probe is now commonly used by the obstetrician/gynecologist. The improved resolution offered by the probe makes it easier to study the anatomic development of the first trimester fetus in greater detail. The aim of this study was to define the gestational age at which certain fetal structures become apparent by ultrasound and to screen pregnancies at high risk for development of fetal anomalies that could be detected in the first trimester. Endovaginal ultrasound was performed on 60 pregnant women at 8 to 13 menstrual weeks. Clinical follow-up disclosed 36 normally developed fetuses at delivery, five abnormal scans, and 19 ongoing pregnancies. The results of this study show that it is possible to demonstrate most of the major fetal structures by 13 weeks' gestation. By imaging the fetus transvaginally, detection of fetal anomalies can be accomplished much earlier than with the transabdominal scanning alone.