The overall efficiency of cloning has stayed low since this technique appeared. Most of the losses in the bovine species take place in early gestation between Day 35 and Day 70, when deficient placental development has been described. Late fetal losses are associated with excessive fetal growth and placental hydrops (Large Offspring Syndrome or LOS). One study measuring crown-rump length (CRL) by ultrasound (US) did not show any difference between clones and controls (Pace et al., 2002). The objective of this work was to compare fetal and placental measurements at Days 34, 50, and 64 for bovine clones and control pregnancies to determine whether these could be predictive of a further development of LOS. Twenty-five clone and 32 control (28 AI and 4 IVF) singleton Holstein pregnancies were used for US with a 5-MHz rectal probe. Clones originated from adult skin fibroblasts (three genotypes), used after serum starvation, as previously published (Vignon et al., 1998). CRL and head length (HL), orbital diameter (OD), vesicle width (VW), and length and width of the placentome closest to the fetus were measured at each stage. CRL were also recorded from six clone, six IVF and five AI, Day 34 and Day 60 fetuses recovered at slaughter. Maternal clinical parameters, US images with increased fetal fluids, excessive weight, and clinical features at surgical removal or birth were used to diagnose LOS. Data were analysed using multiple regression analysis with SAS software. There were no differences between IVF and AI fetal and placental measurements by ultrasound and the two groups were pooled as a single control group. LOS was diagnosed in 29% of the clones. CRL and HL were significantly smaller in clones at all stages (CRL: 10.2 ± 3.8 mm, n = 5 v. 13.6 ± 2.4 mm, n = 7, at retrieval at Day 34; 31.8 ± 5.6 mm v. 36.0 ± 4.6 in controls at Day 50, by US, and 48.6 ± 11.4 v. 63.3 ± 4.9 at Day 64, by US, P < 0.05, in clones and controls, respectively) but there was no difference between the clones developing LOS and those that did not. There was no difference for OD or VW at any stage. Placentome width but not length was statistically smaller in clones compared to controls (4.8 ± 1.5 v. 7.2 ± 1.7 mm at Day 50 and 5.7 ± 2.0 v. 9.4 ± 4.2 at Day 64, in clones and controls, respectively, P < 0.05). There were only two clones retrieved at Day 64, one degenerated and the other similar to controls. Placentome development was delayed. These data clearly show that although a large proportion of clones develop LOS in late gestation, they are actually smaller than controls in early pregnancy, whether or not they will develop LOS. This is probably due to delayed or abnormal early placental development, which can be detected by US. US cannot be used, however, to predict further development of LOS, and other means such as maternal plasma PSP60 concentrations (Heyman et al., 2002) must be used.