A cross-sectional study was conducted in 1991 on 433 workers of a cotton mill in Bahar Dar, northern Ethiopia. The study consisted of symptom evaluation using a standardized questionnaire, lung function tests, chest x-ray, and measurement of dust concentration in the various work areas. A hundred non-exposed hospital workers were included as control group. The overall prevalence of byssinosis among the exposed subjects was 45.5%, being highest among carding (57.9%) and ring frame workers (57.1%). Lower prevalences were found in weavers (36.7%) and those working in the preparatory unit (32.1%). Chronic bronchitis occurred in 48.8% of workers in the carding section, and in none of the control group. Bronchial asthma occurred in 11.5% of workers in the carding and ring frame sections, and in 28.6% of the workers in the waste section. Twelve per cent of the control group had bronchial asthma. Tuberculosis was prevalent in 5.3% of the mill workers and in 2.1% of the control group. Ventilatory capacity (FEV1 and FVC) was significantly reduced in the exposed workers (p < 0.05). The study revealed that the prevalence of byssinosis and other respiratory disorders was extremely high among the cotton mill workers. In view of the above findings preventive measures deserve a high priority.