Brucellosis is known to occur in Yemen but its epidemiology has not been extensively studied. The present investigation examined risk factors for human brucellosis in Yemen using a hospital-based case-control study. A total of 235 consecutive patients with brucellosis attending the Central Health Laboratory in Sana'a, Yemen, were matched in respect of age, sex, and place of residence, rural or urban, with 234 controls selected from individuals attending the Central Health Laboratory for unrelated health problems. Clinical information on patients and controls was supplemented with occupational and socio-economic data obtained by interview of cases and controls using a standard questionnaire. After controlling for confounding factors significant risk factors for infection related to occupation as a farmer (OR 2.5 (95% CI 1.4-4.5, P < 0.0001)), shepherd (OR 7.8 (95% CI 1.0-61, P 0.05)) or microbiologist (OR 24.5 (95% CI 2.9-204, P 0.003)); and drinking fresh milk (OR 2.0 (95% CI 1.3-4.3, P 0.001)) and laban (OR 22.7 (95% CI 1.7-4.2 P < 0.0001)). Taking other milk products and offal were not risk factors. Socio-economic and educational factors were also independent risk factors. Occupational, food and socio-economic risk factors significantly confounded one another. Yemen shares some but not all of the risk factors of neighbouring countries. The interrelation between the various factors is complex and studying any one in isolation may give a false impression of its public health significance. Control through education of the population to minimize exposure to, and contact with, animals and their milk and milk products and to boil milk before drinking it or using it to make buttermilk, would be difficult as these would represent such fundamental changes to established patterns of behaviour of this society. Ideally there would be a campaign to control the infection by animal vaccination but the costs and logistic difficulty would be great. Presently there is a clear need for doctors in Yemen to be made aware of the frequency of this infection, the means available for clinical and laboratory diagnosis and effective treatment, while strategies to control the disease in Yemen are formulated and field tested.