Background.Childhood tuberculosis (TB) is difficult to diagnose reliably because signs and symptoms are nonspecific and sputum for direct microscopy is difficult to obtain, especially in very young children. This diagnostic dilemma is thought to have increased with the HIV pandemic. Few studies on treatment outcome of dually infected children in high endemic countries have been reported. This study examines the impact of HIV infection on clinical presentation, diagnostic criteria and treatment outcome of TB in Ethiopian children.Methods.A prospective cohort study of children with TB diagnosed in Addis Ababa from December 1995 to January 1997 in which HIV-positive children were compared with HIV-negative children with regard to medical history, signs and symptoms, nutritional status, chest radiography, tuberculin skin test, response to TB treatment and final outcome.Mycobacterium tuberculosiswas cultured in children with pulmonary manifestations.Results.HIV-positive children were younger, were underweight and had a 6-fold higher mortality than HIV-negative children. The tuberculin skin test was less sensitive and chest radiography was less specific in HIV-infected patients. Adherence to treatment was high (96%), and the cure rate was 58% for HIV-positive and 89% for HIV-negative TB patients.Conclusion.HIV-positive children are at risk of diagnostic error as well as delayed diagnosis of TB. TB manifestations are more severe and progression to death is more rapid than in HIV-negative children. Weight for age may be used to identify children at high risk of a fatal outcome.