Background:To compare the effectiveness of a theory-based lifestyle physical activity (PA) program delivered to individuals with type 2 diabetes in diabetes education centers by professionals and peers.Methods:Changes over 16 weeks in PA (steps/day) and related variables (weight, waist girth, resting heart rate, systolic and diastolic blood pressures) were compared (RMANOVA) for two groups: 157 participants led by 13 different professionals versus 63 participants led by 5 peer leaders.Results:Overall, the 81 male and 139 female participants (age = 55.7 ± 7.3 years, BMI = 35.2 ± 6.6) showed an incremental change of 4,059 ± 3,563 steps/day, which translates into an extra 37 minutes of daily walking (P < .001). Statistically significant improvements were also seen in weight, waist girth, and blood pressure (all P < .001) and resting heart rate (P < .05). There were no significant differences in outcomes between professional and peer-led groups.Conclusions:A theory-based behavior modification program featuring simple feedback and monitoring tools, and with a proven element of flexibility in delivery, can be effective under real-world conditions while addressing inevitable concerns about resource allocation. Program delivery by peer leaders, in particular, could address a potential obstacle to dissemination by helping to alleviate existing high caseload demands on diabetes educators.