All patients presenting at one consultant booking antenatal clinic had a routine real-time ultrasonic scan. The purpose was to study the accuracy of the technique, the additional work involved and the clinical benefit. All scans were performed by one operator. The average time per scan was 6 min compared with 15 min for each B scan. When gestation assessed by scan differed from gestation assessed by menstrual dates or clinical examination, an independent assessment was made after birth. There was a marked decrease in utilization of B-scanning facilities. Routine real-time scanning at the first visit was a reliable method of assessing gestation in 94% of patients.