OBJECTIVE: To compare clinical and histologic characteristics of papillary thyroid carcinomas (PTCs) ≤10 mm in patients ≤21 years old with larger ones and with microcarcinomas in adults.STUDY DESIGN: Retrospective study of patients with PTC diagnosed between 1983 and 2012. Medical records were reviewed and information about age, sex, tumor size, intra/extrathyroid extension, lymph node, and distant metastases were collected.RESULTS: Patients ≤21 years old (n = 93) and adults (n = 1235) with PTC were identified. Among the former, 34 had PTC ≤10 mm (37.4%) and among the latter, 584 had papillary thyroid microcarcinoma (PTM) (47.3%), P = .082. Patients with tumors ≤10 mm less frequently had extrathyroidal extension and lymph node metastases compared with larger tumors (8.8% vs 33.3%, P = .017, and 60.0% vs 95.2%, P = .001, respectively). The percentage of PTC ≤10 mm increased with age (7.1%, 32.0%, and 48.1% in age groups ≤15, 15-18, and >18 to ≤21 years old, respectively; P = .016). Mean tumor size was larger (6.8 ± 2.7 vs 5.8 ± 2.8 mm, P = .030), and lymph nodes metastases were more frequent (41.2% vs 18.6%, P = .003) in patients ≤21 years of age compared with adults with PTM. The frequency of multifocal cancers decreased between 1983-1992, 1993-2002, and 2003-2012 (66.7%, 53.6%, and 27.1%, respectively, P = .019).CONCLUSIONS: The frequency of PTC ≤10 mm is low in children, increases in adolescents, and reaches that of adults at 18-21 years of age. Mean tumor size is larger and metastases to regional lymph nodes more frequent in comparison with PTM in adults. Whether their treatment and follow-up could be based on guidelines used for PTM in adults is questionable.