After the accident at the Chernobyl nuclear power plant, a considerable increase in the incidence of thyroid cancer among children in Belarus was observed. In the present study, the frequency of the c-ret protooncogene rearrangements in samples of thyroid carcinomas resected and diagnosed in 1998 from individuals in Belarus was investigated. The ret/PTC1 oncogene was detected in 19% of the samples, and the ret/PTC3r1 oncogene, in 14%. The number of ret/PTC1 rearrangements observed in tumor cells from the patients whose age at the time of the accident was from 1 to 10 years, was greater compared to those whose age at the time was from 10 to 20 years, irrespective of the year of surgery (1996 or 1998). The majority of the patients with ret/PTC3r1 rearrangements lived in Gomel oblast, which was contaminated by the Chernobyl meltdown.