A survey of thyroid and breast diseases was performed in 477 women representative of a middle-aged female population in Malmö, Sweden. Fifty-four women (11.3%) were found to have palpable goitre; 45 of these were unaware of their disorder. All goitres were considered to be benign. One woman with goitre had a mild thyrotoxicosis; the goitres in the other 53 women were atoxic. Seventy-six women (16.0%) had been subjected to surgical breast biopsy 1-25 years before the present survey (median 9 years). The histological diagnoses were: cancer 1, fibroadenoma 8, cystic disease 48, fibrosis 9, and miscellaneous 10. A correlation between atoxic goitre and histologically verified benign breast disease was found (p less than 0.05). The correlation was explained solely by an association between goitre and fibrosis of the breast (p less than 0.001). This study shows a correlation between fibrosis of the breast and atoxic goitre in middle-aged women. The correlation is considered to be a true one, and a possible explanation is briefly discussed.