This study examined sleep changes following cessation of marijuana and alcohol use during late adolescence. Twenty-nine heavy marijuana and alcohol users and 20 matched controls were studied during a 28-day monitored abstinence period. Sleep was examined as a function of prior substance use during Nights 1-2 and Nights 27-28. On Night 2, percent rapid eye movement sleep was predicted by past month alcohol use, whereas percent slow wave sleep was predicted by marijuana intake. By Night 28, neither alcohol nor marijuana use predicted any sleep architecture measure. However, on Night 28, indices of period limb movements (PLMs) in sleep were predicted by marijuana and alcohol intake. Results indicate that in adolescents: (1) cessation of heavy marijuana and alcohol use may influence sleep; (2) most sleep abnormalities abate within several weeks of abstinence; and (3) PLMs may increase following abstinence.