Ultrasound assessments of fetal growth have been used in other species of primates to estimate fetal age, but there are no published morphometrics for the St. Kitts green monkey (Chlorocebus sabaeus), a species that has been important for studies of transplantation of fetal tissue into the brain as potential treatment for degenerative disease. Previous studies with other primate species have used relatively small numbers of pregnancies, measured repeatedly, to derive regressions for predicting fetal age from ultrasound studies. The present study derives data from 967 pregnancies, collected over a 9-year period, for predicting fetal age from ultrasound measurements of crown rump length, biparietal diameter, head circumference, abdominal circumference, and femur length in the St. Kitts green monkey. Linear and polynomial regressions were determined from pregnancies dated from a 3- to 4-day breeding period and confirmed in a second, independent group of pregnant monkeys with more extended breeding times to determine their accuracy for predicting fetal age. Although similar to morphometrics reported in other monkey species, there were some significant differences. These data will improve the estimates of fetal ages in previously published studies of St. Kitts green monkeys and provide more precise estimates of fetal age in studies of fetal development, genomics, and reproductive toxicology. Am. J. Primatol. 74:433-441, 2012. © 2012 Wiley Periodicals, Inc.