To investigate the prevalence of thyroid dysfunction, autoimmune thyroid disease (AITD), and simple goiter at goiter diagnosis, and to analyze the natural course of simple goiter and predictors for progression to AITD and/or thyroid dysfunction.

In total, 939 patients (770 females, 5.0-17.9 years) with goiter were reviewed retrospectively. Anthropometrics, pubertal status, goiter grade, and family history (FH) of thyroid disease were investigated. Simple goiter was defined as euthyroid goiter without pathologic cause, after excluding AITD and isolated nonautoimmune hyperthyrotropinemia (iso-NAHT).

At diagnosis, 36.9% of children showed thyroid dysfunction and/or AITD (euthyroid AITD [9.9%], hyper- or hypothyroid AITD [18.4%], iso-NAHT [8.6%]). Risk for subsequent medication was higher in euthyroid AITD than simple goiter (20.4% vs 0.3%, P < .001). Hashimoto thyroiditis (HT) and iso-NAHT developed in 5.2% and 6.6% of patients initially diagnosed with simple goiter during the median 2.0-year follow-up. Compared with the persistent simple goiter group, the HT group had greater FH (54.8% vs 23.6%) and unchanged or increasing goiter size (89.3% vs 71.8%), and the iso-NAHT group had a higher proportion of patients within the upper tertile range of baseline thyrotropin levels (71.8% vs 24.9%) and unchanged or increasing goiter size (86.8% vs 71.8%; all P < .05).

Thyroid disorders were detected in one-third of pediatric patients presenting with goiter. The higher risk for thyroid dysfunction needing medication in patients with euthyroid AITD emphasizes the importance of autoantibody evaluation at diagnosis. During simple goiter follow-up, progression to HT or iso-NAHT occurs, especially in patients with FH or persistent goiter.