The authors measured prevalence of byssinosis in spinning and textile workers of Karachi, Pakistan, and examined association of the disease with demographic and environmental factors. This was a cross-sectional study conducted in 3 spinning and textile mills and 3 colonies inhabited by spinning and textile workers. A precoded questionnaire was administered to the workers and followed by physical and clinical examination. Among 362 textile workers, the authors found the prevalence of byssinosis to be 35.6%. Educational status of the workers and section of the mill were significantly associated with prevalence of the disease. The authors conclude that there is a high prevalence of byssinosis in spinning and textile workers of Karachi. Furthermore, low education level and work in the spinning section of the mill appear to contribute significantly to the high prevalence of the disease in Pakistan.