Perfluorooctanesulfonate (PFOS) is a widespread environmental contaminant emanating from the production and/or metabolism of fluorinated chemicals with a variety of applications. The goal of this work was to assess the toxicity and bioconcentration of PFOS in the fathead minnow (Pimephales promelas). Sexually mature fish were exposed via the water for 21 d to 0 (control), 0.03, 0.1, 0.3, or 1 mg PFOS/L, and effects on reproductive capacity and endocrinology were assessed. To determine possible developmental effects, a subset of embryos from parental exposures at each test concentration were held for an additional 24 d in the same PFOS treatments. A concentration of 1 mg PFOS/L was lethal to adults within two weeks. The 21-d 50% effect concentration (95% confidence interval) for effects on fecundity of the fish was 0.23 (0.19–0.25) mg PFOS/L. Exposure to PFOS caused various histopathological alterations, most prominently in ovaries of adult females. Adult males exposed to 0.3 mg PFOS/L for 21 d exhibited decreased aromatase activity and elevated concentrations of plasma 11-ketotestosterone and testosterone. No significant adverse effects on survival or growth were observed in developing fathead minnows held for 24 d at PFOS concentrations up to 0.3 mg/L. Adult fathead minnows readily accumulated PFOS from the water. The largest concentrations of PFOS were in blood, followed by liver and then gonad; for all tissues, females accumulated higher concentrations than males. Water and tissue concentrations of PFOS associated with effects in this study exceeded those reported for samples collected from the field by two to three orders of magnitude, suggesting that the current risk of PFOS on aspects offish reproduction and development assessed in this study would be small.