To identify some dynamic or morphological patterns for the diagnosis of small bowel obstruction by hernia, adhesions or volvulus, we submitted to ultrasonography (US) 61 patients with clinical and radiographic syndromes of mechanical small bowel obstruction. The cause of obstruction was demonstrated in 58 patients-namely, with surgery in 56 patients and further instrumental examinations in 2. Three patients died before surgery. In our series, small bowel obstruction with strangulation was demonstrated at surgery in 31/56 patients. In 27/31 patients, US showed the coexistence of dilated loops with different kinetic behavior in the abdominal cavity-i.e., the simultaneous presence of akinetic loops with an intraluminal fluid-fluid level by sediment and peristaltic loops with solid particles in suspension. In 4/31 patients with strangulating small bowel obstruction. US provided no useful elements to explain the mechanism of obstruction. The US pattern of fluid-fluid levels due to intraluminal sediment in all the intestinal mass above the occluded segment was observed in 6/6 patients with uncompensated mechanical intestinal obstruction. This sign is due to the absence of intestinal muscular activity in the late stages of mechanical intestinal obstruction; its value is purely prognostic. To conclude, the US pattern of fluid-fluid levels by sediment diffused in the whole intestinal mass provides no useful elements to explain the cause of obstruction: on the contrary, the US pattern characterized by isolated intraluminal fluid-fluid levels or by the association of akinetic and peristaltic loops in the abdominal cavity appears pathognomonic of strangulating obstruction caused by volvulus, adhesion or hernia, with 87% sensitivity and 100% specificity.