The incidence of antithyroglobulin autoantibodies (ATA) was 17.7% in 963 patients (who attended the clinic from 1981 to 1990) with differentiated thyroid carcinoma (DTC). Another 12 patients developed ATA for a transient period after the treatment with radioiodine. The prevalence of ATA in females (21.5%, 123/572) was significantly higher (p < 0.001) than that seen in males (12.0%, 47/391). Age-dependent occurrence of ATA was not seen for the various age decades. The ATA was more prevalent (p < 0.01) with the papillary type of tumor (118/564) as compared to the follicular variety (51/398). ATA did not influence the metastatic spread of the tumor at the initial presentation (105/170 for the ATA-positive group and 445/793 for the ATA-negative group). However, within the group with metastases, 82.9% (87/105) of patients had local spread into the neck in the presence of ATA, which was significantly higher (p < 0.01) than that seen for patients without ATA (63.8%, 284/445). For assessment of the influence of ATA on the outcome of the disease, the data from 222 patients (46 positive and 176 negative for ATA), with a minimum follow-up of 5 years (mean follow-up of 7.4 years), was considered suitable for analysis. The outcome of the disease was comparable in the presence and the absence of ATA (38/46 and 137/176 patients became disease-free in ATA-positive and -negative groups, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)