A 10 year-old mare presented for sudden onset hind limb lameness. The mare was non-weight bearing on the right hind limb and within 24 hrs there was significant swelling centered over the right gluteal region. In Figure 1, the pelvis of a horse is pictured to identify the left (bottom blue arrow) and the right (top blue arrow) coxofemoral joints. In Figure 2 and 3, the pelvis has been rotated slightly to picture the area that is most commonly ultrasounded to assess the coxofemoral joint space. In Figure 3, the red line corresponds to the junction of the pelvis and the femor. The blue arrow corresponds to the coxofemoral joint space.