(Aim) According to the surveillance, new cases of thyroid cancers in the young population have increased. The thyroid ultrasound screening for children aged 0-18 was performed in Fukushima after the accident at the Fukushima Daiichi Nuclear Power Plant. As a result, many thyroid cancer cases in the young population have been found. To explore the carcinogenic mechanisms of the cancers, we analyzed their clinicopathological and genetic features. (Methods and Results) We analyzed 138 patients (52 males and 86 females) operated between 2013 and 2016 at Fukushima Medical University. The median age at operation was 18 years old. The mean size of the tumors was 15.3mm. The lymph node metastasis was observed in 109 (79.0%) cases. We analyzed BRAF(V600E) mutation by direct DNA sequencing. The BRAF(V600E) mutation was observed in 96 (70.0%) cases of the thyroid cancers. On the contrary, the RET/PTC3 rearrangement was observed in 1 (0.7%) cases. (Conclusion) The RET/PTC3 rearrangement has been found in pediatric post-Chernobyl thyroid cancer. However, the RET/PTC3 rearrangement with PTC was detected only 0.7% in our cases. The prevalence of the BRAF(V600E) mutation was comparable to Japanese adult sporadic cases, implying that the carcinogenesis mechanism may be similar between young population and adult papillary thyroid cancers.