Background and Purpose. The objective of this review was to construct an updated evidence-based clinical practice guideline on the use of physical activity and diet for the management of osteoarthritis (OA) in adults (>18 years of age) who are obese or overweight (body mass index ≥25 kg/m2). Data Sources. Articles were extracted from the following databases: MEDLINE, EMBASE (Current Contents), SPORTDiscus, SUM, Scopus, CINAHL, AMED, BIOMED, PubMed, ERIC, the Cochrane Controlled Trials, and PEDro. Study Selection. The Ottawa Panel and research assistance team strictly applied the inclusion and exclusion criteria from previous Ottawa Panel publications. Data Extraction. An a priori literature search was conducted for articles related to obesity and OA of the lower extremities that were published from January 1, 1966, to November 30, 2010. Inclusion criteria and the methods to grade the recommendations were created by the Ottawa Panel. Data Synthesis. Recommendations were graded based on the strength of evidence (A, B, C, C+ D, D+ or D-as well as experimental design (I for randomized controlled trials and II for nonrandomized studies). In agreement with previous Ottawa Panel methods, Cochrane Collaboration methods were utilized for statistical analysis. Clinical significance was established by an improvement of ≥15% in the experimental group compared with the control group. There were a total of 79 recommendations from 9 articles. From these recommendations, there were 36 positive recommendations: 21 grade A and 15 grade C+ There were no grade B recommendations, and all recommendations were of clinical benefit. Limitations. Further research is needed, as more than half of the trials were of low methodological quality. Conclusions. This review suggests that physical activity and diet programs are beneficial, specifically for pain relief (9 grade A recommendations) and improved functional status (6 grade A and 7 grade C+ recommendations), for adults with OA who are obese or overweight. The Ottawa Panel was able to demonstrate that when comparing physical activity alone, diet alone, physical activity combined with diet, and control groups, the intervention including physical activity and diet produced the most beneficial results.