An outbreak of mainly extrapulmonary tuberculosis (TB) in a group of about 550 patients with rheumatoid arthritis (RA) is described. These patients had been attending the practice of a former general practitioner who treated cases of rheumatoid arthritis with phenylbutazone and steroids. The number of diagnosed TB cases was 55. Six cases had a contagious lung localisation. The possible sources of the outbreak were analysed. Both a visit on a same day as a sputum positive patient (chi 2-trend: 20.4; p < 0.001) and the administration of steroids (odds ratio (OR): 36.2; 95% confidence interval (CI): 8.8-313) were independent risk factors. There also appeared to be a relationship between TB and RA (OR: 4.4; 95%-BI: 2.2-9.1). Exogenous re(infection) and endogenous reactivation are possible causes of this outbreak.