Background: physical activity studies in older people often have poor recruitment. Including a questionnaire with the invitation would provide information about non-participants and selection bias, but could reduce recruitment. Telephone contact might encourage participation.

Objective: to test the effects of different strategies for recruitment into a study of physical activity in older people.

Design: factorial randomised controlled trial. Randomisation by household into four groups: telephone contact plus questionnaire, telephone contact only, questionnaire only, neither.

Setting: primary care, Oxfordshire, United Kingdom.

Participants: 560 patients 65 years randomly selected after exclusions.

Interventions: questionnaire to assess health, functional ability and physical activity. Telephone contact by the research nurse a week after sending study information.

Main Outcome Measure: recruitment into physical activity study.

Results: telephone contact increased recruitment: contact 47.9% (134/280), no contact 37.9% (106/280), difference (adjusted for the clustering effect of household) 10.0% (95% CI 0.2-19.8). Questionnaire inclusion did not significantly reduce recruitment: no questionnaire 44.3% (124/280) questionnaire 41.4% (116/280) difference –2.9% (95% CI –12.7–7.0).

Conclusions: telephone contact significantly increased recruitment and should be considered in studies where recruitment may be low. While inclusion of a questionnaire provided valuable information on non-participants and did not significantly reduce recruitment, an adverse recruitment effect could not be excluded.