Since 1983 annual surveys have monitored disease incidence and severity in commercial cotton crops in the major production areas of New South Wales (NSW), Australia. Significant epidemics of bacterial blight and Verticillium wilt have occurred during this period. Major epidemics of black root rot and Fusarium wilt are now developing. The relationship between average annual lint yields and disease incidence or severity is investigated at the state, regional and local level. Seasonal weather conditions (droughts, floods, wet harvests, cool springs, etc) appear to have had a greater impact than disease on average lint yields.