The objective of this study was to describe the sonographic anatomy of the placenta and to determine its in vivo development during normal pregnancy in cows. All examinations were performed transrectally using an 8 MHz linear transducer. Thickness and appearance of the endometrium, myometrium and myometrium below the placentomes, length and width of placentomes as well as of the stalks of placentomes and their shape, the distance between the tip of stalk of placentomes and the farthest point of the placentome and the thickness of the hyper-echodense border of the placentomes were assessed in different areas of the uterus: close to the cervix, close to the uterine corpus, in the region of the horn and close to the tip of the pregnant and non-pregnant uterine horn. The size of placentomes increased steadily until week 27 of gestation followed by a slight increase until week 31 of gestation and stagnated afterwards through term with reaching a plateau in the growth curve. In the non-pregnant horn smaller placentomes were found compared to the pregnant horn. Placentomes in the area of the tip of the pregnant horn were smaller than those in the area of the horn, corpus or close to the cervix. The hyper-echodense borders of the placentomes, the endometrium and myometrium showed no alterations throughout pregnancy. Ultrasonographic monitoring of pregnancies, especially examinations of placentae may be a valuable diagnostic tool to assess bovine placentae.