Introduction: In 1973-74, Michigan residents were exposed to polybrominated biphenyls (PBBs) through an accidental contamination of the food supply. This cohort of exposed individuals and their children has been followed for over 40 years and the population remains highly exposed. There is evidence that exposure to halogenated compounds such as PBBs and polychlorinated biphenyls (PCBs) may interfere with thyroid function. Methods: Between 2004-2014, serum PBB and PCB congeners were measured in 466 women (ages 18-86) who completed questionnaires on health conditions including physician-diagnosed thyroid disease; behaviors; and demographics. Thyroid hormones are also being measured in a subset of women not on thyroid-disrupting medication (N=391). Logistic regression was used to estimate the associations between serum levels of PBB and PCB congeners, considered both individually and grouped according to chemical structure, and thyroid disease. Results: PBB-153 was detected in the serum of 93% of women (median=0.23 ng/mL, interquartile range (IQR)=0.06-0.48), whereas PBB-77, 101 and 180 were detected in <5%. PCB-153, 138, 118 and 180 were detected in >99% of samples and were summed (∑PCB; median=0.71 ng/mL, IQR=0.30-1.20). Ninety-six women (20.6%) reported a physician-diagnosed thyroid condition after the contamination event, and 44 specified a diagnosis of hypothyroidism. PCB congeners and ∑PCB were not associated with any thyroid conditions, but an IQR increase in PBB-153 was associated with increased odds of hypothyroidism, although the estimate for any thyroid condition was closer to the null (adjusted odds ratio (aOR)=1.50, 95% confidence interval (CI): 1.0, 2.3 and aOR=1.13, 95% CI: 0.8, 1.6, respectively). Ongoing measurement of thyroid hormones in this cohort will allow for the assessment of possible subclinical thyroid dysfunction, and results will be reported. Conclusions: These results suggest that PBB-153 exposure may influence thyroid function in women.