A 20-year-old asylum seeker presented with vomiting and left thigh pain, with a biological inflammatory syndrome. Pregnancy was diagnosed. Investigations revealed a pseudo-cystic, 20-cm-long retroperitoneal abscess, biopsy of which confirmed the diagnosis of tuberculosis. Evolution after cyst drainage and under conventional anti-tuberculosis treatment was favourable. An abdominal location of tuberculosis is rare and its diagnosis is difficult especially in countries with a low incidence of the disease. Unexplained abdominal manifestations and/or persistent biological inflammatory syndrome, especially in high-risk groups, should raise the suspicion of tuberculosis.