Objective: To review and provide details about the primary and secondary findings from the Multimodal Treatment study of ADHD (MTA) published during the past decade as three sets of articles. Method: In the second of a two part article, we provide additional background and detail required by the complexity of the MTA to address confusion and controversy about the findings outlined in part I (the Executive Summary). Results: We present details about the gold standard used to produce scientific evidence, the randomized clinical trial (RCT), which we applied to evaluate the long-term effects of two well-established unimodal treatments, Medication Management (MedMGT) and behavior therapy (Beh), the multimodal combination (Comb), and treatment "as usual" in the community (CC). For each of the first three assessment points defined by RCT methods and included in intent-to-treat analyses, we discuss our definition of evidence from the MTA, interpretation of the serial presentations of findings at each assessment point with a different definition of long-term varying from weeks to years, and qualification of the interim conclusions about long-term effects of treatments for ADHD based on many exploratory analyses described in additional published articles. Conclusions: Using a question and answer format, we discuss the possible clinical relevance of the MTA and present some practical suggestions based on current knowledge and uncertainties facing families, clinicians, and investigators regarding the long-term use of stimulant medication and behavioral therapy in the treatment of children with ADHD. [For Part I: "Executive Summary," see EJ798027.]