Active surveillance (AS) for low-risk papillary thyroid microcarcinoma (T1aN0M0, PTMC) was initiated in Kuma Hospital (Kobe, Japan) in 1993 and Cancer Institute Hospital (Tokyo, Japan) in 1995. Thereafter, several manuscripts showing favorable outcomes of the patients have been published from these institutions. After the adoption as a management strategy by guidelines conducted by the American Thyroid Association, many manuscripts with good results have been published from countries other than Japan. To date, some factors have been identified as predictors of PTMC progression such as young age and high thyroid-stimulating hormone level, but none of the patients were reported to show distant metastasis or die of thyroid carcinoma during AS. Conversion surgery (CS) should be done if PTMCs constantly progress during AS, but no difference in recurrence-free survival or overall survival could be detected between patients who underwent CS after AS and immediate surgery. To date, no molecular markers predicting PTMC progression have been identified and AS is an only strategy for discriminating progressive cases. In conclusion, AS is a very useful and safe strategy for the management of PTMC, if appropriately implemented.