 The purpose of the proposed study is to determine the effectiveness of methylphenidate HCl Concerta in college students with ADHD. This study will consist of 110 college students between the ages of 18 and 25 who are enrolled full-time in a local or junior college. The study consists of an 8-week double-blind, placebo-controlled trial of placebo versus methylphenidate HCl Concerta followed by a 10-week extension of open label methylphenidate HCl Concerta. 