In briefEffort thrombosis usually afflicts an extremity and is caused by compression. This case report, in contrast, involves superior mesenteric and left portal vein septic thrombosis in a backpacker following prolonged hiking and abdominal straining. The condition may have been caused by localized splanchnic venous ischemia, erosion of the bowel-blood barrier, and release of bacterial endotoxin in this dehydrated and detrained athlete. Diagnosis of this disorder is aided by noting characteristic abdominal pain, fever, nausea, and vomiting, as well as by imaging with MRI, CT, or duplex ultrasonography. Antibiotics and anticoagulants are key to treatment.