The work processes and main work demands experienced by workers in a pharmaceutical manufacturing industry were evaluated, together with their association with physical and mental disorders. An observational and analytical study was conducted in 244 employees of a drug manufacturing company in Mexico City. The PROESSAT program (worker health assessment and tracking program) was used to collect data on working conditions and adverse health effects.The study population was divided almost equally by gender, with 50.4% males and 49.6% females. Average age was 34.5 years (S.D., 7.9 years). Study demands evaluated included: confusing or unclear supervisor orders, awkward postures, repetitive tasks, working in a single place without moving, rotating shift work, strict quality control, having to concentrate to avoid accidents, strict supervision, prolonged standing and exposure to noise. Adverse health effects examined included: tension headaches, pathological fatigue, sleep disorders, anxiety, migraine, depression, psychosomatic digestive disorders and non-specific cardiovascular disorders. The overall morbidity rate was 83 per 100 workers. Jobs in quality control featured the greatest number of job demands associated with adverse health effects, and men exposed to different demands had a stronger association with adverse health effects than similarly exposed women. Several interventions to reduce the adverse effects on workers and in the company are proposed.