An outbreak of louse-borne relapsing fever, due to the return of soldiers to their original recruitment areas, after the end of thirty years of fighting in northern Ethiopia, was reported in Arsi region, southern Ethiopia. The epidemic spread to different members of the community and eventually the schools. We studied 389 patients affected by the epidemic and who were admitted to Asella Hospital between June 1991 and May 1992. Twenty-seven per cent of the patients were ex-soldiers; 28% were students, who were admitted to the hospital since the schools were opened after the summer vacations. The common clinical features of the disease were fever (99%), headache (92%), hepatosplenomegaly (66%), myalgia (55%), arthralgia (51%), petechial rash (43%), epistaxis (24%) and jaundice (23%). Observed complications were pneumonia (10%), pulmonary edema (6%), myocarditis (3%) and 6 abortions in 15 pregnancies. Patients were treated with low dose penicillin and i.v. fluids. The in-hospital case fatality rate was 3.6%. Jarisch-Herxheimer reaction occurred in 43% of the patients. 1.8% of the patients had relapses after treatment.