In the past decade, there has been no systematic review of the evidence for maintenance of physical activity and/or dietary behavior change following intervention (follow-up). This systematic review addressed three questions: 1) How frequently do trials report on maintenance of behavior change? 2) How frequently do interventions achieve maintenance of behavior change? 3) What sample, methodologic, or intervention characteristics are common to trials achieving maintenance? Systematic review of trials that evaluated a physical activity and/or dietary behavior change intervention among adults, with measurement at preintervention, postintervention, and at least 3 months following intervention completion (follow-up). Maintenance of behavior change was defined as a significant between-groups difference at postintervention and at follow-up, for one or more physical activity and/or dietary outcome. Maintenance outcomes were reported in 35% of the 157 intervention trials initially considered for review. Of the 29 trials that met all inclusion criteria, 21 (72%) achieved maintenance. Characteristics common to trials achieving maintenance included those related to sample characteristics (targeting women), study methods (higher attrition and pretrial behavioral screening), and intervention characteristics (longer duration [>24 weeks], face-to-face contact, use of more intervention strategies [>6], and use of follow-up prompts). Maintenance of physical activity and dietary behavior change is not often reported; when it is, it is often achieved. To advance the evidence, the field needs consensus on reporting of maintenance outcomes, controlled evaluations of intervention strategies to promote maintenance, and more detailed reporting of interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved).