Twenty early pregnancies were diagnosed and monitored in vervet monkeys by ultrasonography. Non‐gravid uteri became increasingly echogenic from cycle days 7 to 26. The first definite sign of pregnancy was a gestational cavity of 2 mm (±0.80) at 33.0 (±1.48) days menstrual age, which was also used to date all subsequent features. Earlier signs, such as an endometrial line swelling or endometrial ‘pregnancy’ ring, as reported for other non‐human primate species, could not be reliably and consistently used to diagnose pregnancy in vervet monkeys. A rapid increase of the gestational cavity size from days 37 to 49 corresponded closely to a rapid increase in plasma progesterone concentration from day 39 to 49. The first yolk sac was recognizable at 38.0 days (±3.10) and measured 3.3 mm (±0.40) in diameter. A heart beat could be detected at 45.5 (±1.73) days and the size of the first measurable embryo at 35 days was 2 mm. The dating of most features was within the range reported for other non‐human primate species.