This study reports on the DNA sequence of a Tc1-like transposable element Tsn1 from lake trout (Salvelinus namaycush). Tcl-like elements were amplified by PCR using an oligonucleotide primer based on the Tdr1 element of zebrafish. One full-length and two partial-length copies of the transposon were sequenced. In addition, partial Tsn1 elements were recovered from PCR reactions run with primers specific to the 3' terminus of the 28S rDNA. However, sequence analysis of cloned fragments found that these sequences were not associated with the rDNA cistron. Sequence comparisons indicate that Tsn1 is a type A element common to both salmonid and cyprinid fishes. The consensus sequence of the full-length element (Tsn1) was 1643 nucleotides with long terminal repeats (LTRs) of 225 nucleotides. Tsn1 contains a transposase coding region corresponding to 340 amino acids that includes all of the functional elements of Tc1-like transposons. Southern analysis found a high proportion of the Tsn1 transposons in the lake trout genome to be full-length copies.