Background <p>Delay in surgery and the impact on survival in thyroid cancer is unclear. We sought to investigate the association between time to surgery and survival in patients with differentiated thyroid carcinoma (DTC) or medullary thyroid carcinoma (MTC).</p> Methods <p>In this retrospective study, we included patients who were diagnosed with DTC(including papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC) and oncocytic thyroid carcinoma (OTC)) or MTC between 2000 and 2021. Data was gathered from the Surveillance, Epidemiology and End Results (SEER) database. And we defined the cutoff period for delayed surgery of DTC was 3 months, while 2 months for MTC. Kaplan-Meier method and log-rank test were used to analyze overall survival (OS) and cancer-specific survival (CSS).</p> Results <p>181588 patients were included in our study. Of which 165,202 (91.0%) were diagnosed with PTC, 9525 (5.2%) were FTC, 4128 (2.3%) were OTC and 2733 (1.5%) were MTC. Comparison of clinical paraments between delayed and non-delayed patients of the four types of thyroid cancer indicated that delayed surgery may alter the clinical characteristics, leading to tumor progression or increased aggressiveness, especially for lymph node metastasis. Meanwhile, delayed surgery (≥3 months) was associated with decreased survival in PTC and FTC, not for OTC. For MTC, delayed surgery (≥2 months) was associated with poorer OS. Additionally, we analyzed the trends in delayed surgery and found that except for an upward trend in PTC, other pathological types showed no significant fluctuations.</p> Conclusions <p>Delaying surgery for DTC and MTC should be avoided, as this could lead to tumor progression or more aggressive behavior and poorer prognosis.</p>