Symmers' periportal fibrosis of the liver is the major cause of morbidity and mortality in Schistosoma mansoni infection. The diagnosis is best established definitively by a wedge biopsy of the liver. The ability of abdominal ultrasonography to diagnose this condition was prospectively compared with two independent pathological examinations of wedge biopsies of the liver. Both pathologists and the ultrasonographer were unaware of the clinical diagnosis and each other's findings. Twenty-eight of 41 patients had Symmers' fibrosis by pathological examination and all were diagnosed correctly by ultrasonography prior to surgery. Symmers' fibrosis was not diagnosed by ultrasound in any of 10 patients without Symmers' fibrosis on biopsy. In 3 patients the diagnosis of Symmers' fibrosis was uncertain because the pathologists disagreed as to its presence. These results confirm the findings of previous studies and establish that ultrasonography is at least as sensitive as wedge biopsy in diagnosing Symmers' fibrosis.