The gestation period in agoutis can range from 104 to 120 days. Knowledge regarding the morphological characteristics of embryos and fetuses is important as a base for studies in reproduction biotechnology, such as in vitro fertilization, embryo transfer and helps in determining congenital anomalies during the development phase. Thus, given the importance and lack of information about agouti embryology, the objective of this study was to characterize the external morphology and define the biometry of embryos and fetuses, at different days of development. Nine females were submitted to daily colpocytology to identify the estrus, confirm mating and identify day zero of the gestation. When the mating was confirmed they were weighed, underwent abdominal ultrasonography and surgery was conducted on the females at the gestational ages of 25, 30, 35, 40, 45, 50, 75 and 100 days. Sixteen embryos/fetuses were weighed and measured. Agouti embryos at 25 days after mating are "C" shaped, with primitive structures, 0.4 +/- 0.01 cm crown-rump and weighed 0.06 +/- 0.01 g; at 30 days after mating the crown-rump was 0.95 +/- 0.07 cm and weighed 0.28 +/- 0.00 g; at 35 days after mating the crown-rump was 155 +/- 0.07 cm and weighed 0.38 +/- 0.01 g; at 40 days after mating the crown-rump was 2.25 +/- 0.21 cm and weighed 1.25 +/- 0.07 g; at 45 days after mating the crown-rump was 3.45 +/- 0.35 cm and weighed 2.75 +/- 0.64 g; at 50 days after mating the crown-rump was 5.0 +/- 0.3 cm and weighed 7.01 +/- 2.6 g; at 75 days after mating, the skin was dark, the crown-rump was 10.0 +/- 0.14 cm and weighed 55.2 +/- 0.07g. At 100 days after mating, the crown-rump was 13.8 +/- 0.49 cm and fetuses weighed 136.7 +/- 9.40g. Based on the morphological data assessed the embryo and fetus age could be assessed and the size and average weight of agouti embryos was established. (C) 2013 Elsevier B.V. All rights reserved.