LINE-1 is the only currently known active autonomous transposon in humans with an estimated 500 000 copies representing 17% of the human genome. LINE-1 propagates itself through a process called retrotransposition, which includes transcription and reverstranscription, to produce new DNA copies. The new produced DNA copies can integrate into new genomic loci. The insertion of LINE-1 is able to cause genetic instability by affecting the expression or regulation of the nearby genes, thus causing dozens of genetic diseases or tumors. In this review, we summarize the recent research progress on the connection between LINE-1 retrotransposition and human tumorigenesis, which might shed light on the biology mechanisms and treatment of the tumorigenesis.