AIM: To report the clinical significance and treatment of Mycobacterium kansasii infection in the context of HIV disease. DESIGN/METHODS: Retrospective case review of all isolates of M kansasii until June 1994. RESULTS: Ten cases of M kansasii were isolated. All but one patient with this infection had clinical symptoms compatible with generalised infection. The majority had chest infections with the organism isolated on induced sputum but not routine sputum. All isolates were sensitive to ethambutol and nine of 10 to rifampicin. All isolates were resistant to isoniazid and pyrazinamide. CONCLUSION: M kansasii is a pathogen in HIV infected patients and should be treated when isolated. Treatment should be with rifampicin and ethambutol but not isoniazid, as has been recommended previously.