Introduction. The current American Joint Committee on Cancer TNM classification for differentiated thyroid cancer (DTC) separates T1 status into T1a and T1b based on a 1-cm cutoff for maximal tumor dimension. In 2009, the American Thyroid Association recommended total thyroidectomy for tumors >1 cm in contrast to the possibility of lobectomy for tumors ≤1 cm. Our aim was to investigate the prognostic significance of a 1-cm tumor cutoff. Methods. From an institutional database of 3,664 patients with DTC, 1,522 patients with T1 tumors without neck disease or distant metastases were identified. Patient, tumor, and treatment characteristics were compared. Disease-specific survival (DSS) and recurrence-free survival (RFS) outcomes were analyzed. Results. Total thyroidectomy rates were similar between patients with T1a and T1b tumors (P = .307). With a median follow-up of 46 months (range, 1-320), there were no disease-specific deaths in the T1a or T1b groups. In total, 18 patients (1.2%) experienced a recurrence. Five-year RFS was comparable for patients with T1a and T1b tumors (98.6 vs 98.6%; P = .224). Conclusion. T1a and T1b tumors have similar prognosis both in terms of DSS and RFS. It seems that a distinction between tumors of <1 and >1 cm is of no prognostic benefit.