Several plastic chemicals adversely affect reproductive ability. This study examined the possible association between employment in the plastics industry and infertility. Dynamic cohorts of economically active women and men were followed for hospital contacts due to infertility in the Danish Occupational Hospitalisation Register, from 1995 to 2005. A person was considered to be at increased risk in a particular year if plastic work was the main occupation in the previous year. Analyses were standardized according to county, socio-economic group, year and age. 107 cases of treatment for female infertility were observed among female plastic workers, as opposed to an expected 87.15 cases, i.e. relative risk was 1.23 (95% CI: 1.01-1.48). For male workers the numbers were 41 respectively 49.9 cases, with relative risk being 0.82 (95% CI: 0.59-1.11). The increased incidence of infertility treatment in female plastics workers motivates more specific studies of reproductive occupational health in the plastics industry.