This study examines to what extent English-speaking adults who have attended a Japanese immersion program in childhood, in which many content subjects are taught in Japanese, can retain their L2 pronunciation ability even if L2 input dramatically decreases after they exit the program. The results show that the immersion graduates still retained their ability to control segmental timing (i.e., voice onset time (VOT), contrast between single and geminate stops in Japanese), although their L2 sounds were not exactly the same as monolingual speakers’.