Major pathways of progression among legal, illegal, and medically prescribed psychoactive drugs from adolescence to young adulthood are described. The data are based on a follow-up cohort of former adolescents representative of high school students in grades 10 and 11 in New York State who were reinterviewed nine years later at ages 24-25. Various models of progression are tested for their goodness of fit. The patterns formerly observed in adolescence involving progression from one class of legal drug (either alcohol or cigarettes) to marijuana to the use of other illicit drugs appear in the transitional period into young adult, with an additional stage, that of prescribed psychoactive drugs. Some differences appear between men and women, with cigarettes more important for women than for men in the total progression.