The clinical significance and potential morbidity of papillary thyroid microcarcinomas (PTMC) is discussed. Particularly the differences between those PTMC identified postoperatively in histological examination (incidentals), and those diagnosed preoperatively (non-incidentals). We retrospectively analysed differences in clinical presentation and course after treatment in these two groups. The study population consisted of 199 patients with PTMC who underwent surgery from 2000 to 2014. Eight patients preoperatively diagnosed of lateral compartment lymph node metastasis (LNM) were excluded, as they were considered suffering a more advanced disease. We compared characteristics, and outcomes between both groups. There were 118 incidental and 73 non-incidental PTMC. Patients with Incidental PTMC were older (55.7 years vs 50.8 years; P=0.01), have smaller tumours (4.3 mm vs 7.9 mm; P=0.001) and lower preoperative TSH (1.87 vs 3.06; P=0.001). Incidence of serological or histological evidence of autoinmunity was not different between both groups. Multifocal disease (46.8% vs 29.8%; P=0.02) and extracapsular invasion (25.6% vs 4%; P<0.001) were most frequently reported in non-incidental neoplasms. One hundred and sixteen out of 122 patients treated with radioiodine had at least 1 year of follow-up (62 incidentals and 54 non-incidentals). One year after radioiodine, eight incidental cases didnt reach remission criteria (undetectable stimulated thyroglobulin and normal high-resolution cervical ecography). Three of them persisted with biochemical disease 1, 2, and 3 years passed, one patient is waiting for surgery to identified cervical adenopathy, two achieved remission after ganglionar surgery plus more radiodine and two without additional treatment. There were two non-incidental patients without remission 1 year after ablation, both without structural disease, persistent 1 and 6 years passed. There was one biochemical relapse after initial remission in the non-incidental group. In our series, incidental and non-incidental PTMC showed differences at presentation, but similar biological behavior in the follow-up after treatment. Remnant disease is more often seen in incidental carcinomas after ablation.