Polychlorinated dioxins, furans and polychlorinated benzene constitute a family of toxic persistent environmental pollutants. In Europe, environmental concentrations increased slowly throughout this century until the late 1980s. Dioxins have been shown to be carcinogenic in animals and humans. In humans, excess risks were observed for all cancers, without any specific cancer predominating. In specific cohorts, excess risks were observed for reproductive cancers (breast female, endometrium, breast male, testis) but, overall, the pattern is inconsistent. In animals, endocrine, reproductive and developmental effects are among the most sensitive to dioxin exposure. Decreased sperm counts in rats and endometriosis in rhesus monkeys occur at concentrations 10 times higher than current human exposure. In humans, results are inconsistent regarding changes in concentrations of reproductive hormones. A modification of the sex ratio at birth was described in Seveso. There exist no data on effects such as endometriosis or time-to-pregnancy. Small alterations in thyroid function have occasionally been found. Increased risk for diabetes was seen in Seveso and a herbicide applicators cohort but, overall, results were inconsistent. Experimental data indicate that endocrine and reproductive effects should be among the most sensitive effects in both animals and humans. Epidemiological studies have evaluated only a few of these effects.