Despite the benefits associated with a physically active lifestyle, many older adults are insufficiently active to achieve health gain, and also exhibit decreased activity levels with age. Insufficient physical activity in this population is associated with increased morbidity, mortality and demand on health care services and expenditure. There is a clear need for effective intervention to encourage physical activity in older adults. The aim of this paper is to describe the development and participant evaluation of a randomized controlled trial of TeleWalk, a telephone-based motivational counseling intervention to encourage physical activity in adults aged 65 years and older. Participants (N = 186, mean age 74 +/- 6 years) were recruited through their General Practitioner (primary care physician) and randomized to either receive eight telephone counseling sessions and related printed materials over 3 months (intervention group) or participate in outcome assessments only (control group). Intervention group participants were mailed an anonymous evaluation questionnaire on intervention completion. A high response rate was achieved (70%). All respondents (100%) agreed or strongly agreed that a good overall level of service and support was provided, and that the counselor was understanding and supportive. Nearly all respondents agreed or strongly agreed that the service was professional, the counselor advice was helpful and motivating and the information provided was relevant (97, 95 and 89%, respectively). Most (87%) agreed or strongly agreed that the telephone calls encouraged them to be physically active. Among the participants who received printed material, most agreed or strongly agreed that these encouraged them to become or remain active. Findings from this evaluation can be used to inform such interventions and ensure their relevance to community-dwelling older adults.