BACKGROUND The incidence of thyroid cancer is increasing globally. This is mainly due to the increase in the detection of small papillary carcinomas, including papillary microcarcinomas (PMC) 1 cm or smaller. It was suggested recently that PMCs are overdiagnosed and overtreated. METHODS In 1993, the author proposed a clinical trial to compare surgery and observation for low-risk PMC at doctors' meeting in Kuma Hospital, which was approved and the trial started in the same year. Patients choose immediate surgery or observation. This paper shares our 22-year experience with the active surveillance of more than 2000 patients with low-risk PMC and compares the outcomes of immediate surgery with that of active observation. RESULTS The oncological outcomes of these management groups were similarly excellent. In our active surveillance trial on 1235 patients, 8% of patients showed tumor enlargement by 3 mm or more at 10 years of observation, and 3.8% of the patients showed novel appearance of lymph node metastasis at 10 years. Patients 40 years or younger tended to show progression of the disease. Patients with these slight progressions of the disease were successfully treated with a rescue surgery. None of the patients in both study groups died of the disease. However, incidences of unfavorable events, such as temporary vocal cord paralysis (VCP) and temporary and permanent hypoparathyroidism, were significantly higher in the immediate surgery group than in the observation group (4.1 vs. 0.6%, p < 0.0001; 16.7 vs. 2.8%, p < 0.0001; and 1.6 vs. 0.08%, p < 0.0001, respectively). Permanent VCP occurred in two of the surgery group. CONCLUSIONS As a result, although we still offer two options, immediate surgery or observation, to patients with low-risk PMC at Kuma Hospital, we now strongly recommend observation as the best choice.