Loggerhead sea turtles (Caretta caretta) are among the most frequent victims of bycatch in drifting longlines, and the ingestion of fish hooks and fishing lines is one of the most frequent causes of death of sea turtles. The aim of this study was to evaluate whether coelomic ultrasound (US) can be decisive, not only for diagnosis but also to optimize surgical planning based on preoperative evaluation of the bowel conditions and, in addition, to see if there are characteristic sonographic findings in sea turtles associated with the ingestion of fishing lines. Physical examination, hematology, blood chemistry, radiographs, and US examination were performed in 37 loggerhead sea turtles with suspected or known ingestion of fish hooks or monofilament fishing lines. During the ultrasonographic examinations, the loggerhead sea turtles were placed in dorsal recumbency and the prefemoral left and right acoustic windows were used. Nine wild loggerheads had sonographic findings of intestinal and coelomic abnormalities, and the sonographic images were compared with the surgical findings. Ultrasonography positively identified the foreign body in 89% (8/9) animals. The presence of intestinal plication (in all loggerhead turtles) and ultrasonographic visualization of the linear foreign body was always consistent with the ingestion of a fishing line. In sea turtles, fishing lines cause a corrugated appearance in the small intestine due to increased/unproductive peristalsis. The affected small bowel loops are usually dilated with fluid. In the present study, coelomic US allowed us to make a thorough evaluation of the characteristics, number, and severity of the bowel wall lesions in the animals, thus ensuring the planning of a correct surgical procedure. We suggest that US examination of the coelomic cavity should be complementary to radiographic survey in cases of suspected ingestion of fish hooks and fishing lines by sea turtles.