Ninety-six cases of human hydatidosis caused by Echinococcus granulosus were diagnosed from surgical records of hospitals in Theqar Province, Southern Iraq during 1989. The infection rate was higher in female than in male patients (56 versus 40 cases) and increased with their age (maximum, 25.0% in a female group of 31-40 years and 32.5% in a male group of 41-50 years) . Many organs such as liver, lungs, peritoneum and spleen were involved, but the liver was most frequently affected. Of 96 patients, 66 (68.8%) showed single organ-involvement and 30 (31.2%) multiple organ-involvement. In 50 stray dogs surveyed for E. granulosus the prevalence was found to be 56.0% with a mean worm burden of 5, 300. The light infection (1-200 worms) was found in 10.7% of the infected dogs, the medium (201-1, 000 worms) in 21.4% and the heavy (over 1, 000 worms) in 67.9%.