The retinoblastoma (Rb) family consists of the tumor suppressor Rb/p105 and related proteins p107 and Rb2/p130. Although the involvement of the RB/p105 gene in Adult T-cell leukaemia/lymphoma (ATL) has been studied, no mutational data is reported regarding the RB2/p130 gene in ATL. We screened for mutations of the RB2/p130 gene. Mutation was detected in 1 of 41 primary ATL sample. This is the first report describing mutation of the RB2/p130 gene in ATL, suggesting that RB2/p130 may be involved in the development of ATL, and may behave as a tumor suppressor gene in T lymphocytes.