The Occupational Health Branch (OHB) of the California Department of Public Health aimed to characterize and prevent work-related asthma (WRA) and occupational pesticide illness (OPI) in California by developing a program of surveillance and intervention over a 5 year period. This was accomplished through a comprehensive program funded by a cooperative agreement from the National Institute for Occupational Safety and Health (NIOSH). The WRA and OPI program sought to describe and monitor trends using surveillance, to conduct both case-based and targeted worksite investigations in high risk occupations, to develop and provide prevention recommendations, to further develop collaborations that enhanced program impact, and to evaluate the program to ensure effectiveness . Key findings and accomplishments include: (1) A comprehensive surveillance system which identified over 3,100 cases of WRA and 2,700 cases of OPI statewide in 5 years. (2) An evaluation of reporting sources determined that multiple data sources are valuable and lead to improved surveillance. (3) Surveillance and follow-up data collection efforts generated important findings for prevention, including identifying high risk occupations, industries, and exposures. They also documented important information on disability and the impact of WRA and OPI on workers. (4) The overall rate of WRA and over 10 years was 2.3 per 100,000 employed in California. Particularly high rates of WRA were seen among local transit, lumber and wood product manufacturing, electric, gas and sanitary services, heavy construction, health services and social services industries. The highest rates of OPI were seen among nursery workers, pest control operators, and farm workers. Over the duration of the project, OPI and WRA staff conducted nearly 50 work site investigations. These investigations identified several common problems critical for prevention: effective and widely available control measures or alternatives are not installed or used correctly: exposures below regulatory limits (when they exist) may result in pesticide illness and asthma; inadequate training is common; and inadequate communication and regulation lead to unhealthful exposures in workplaces statewide. (5) Many interventions were accomplished, including policy and regulatory recommendations; the development of educational materials with a wide distribution among employers, public health professionals, trade groups, and workers; worker trainings; and the addition of prevention and exposure information into vocational training curricula.