This study compares the efficiency of two methods of recruitment into a randomised controlled trial examining the cost-effectiveness of water therapy for elderly people with lower limb osteoarthritis. The direct cost of recruiting patients via general practice was 27.66 Pounds per patient (1.1 personnel hours/patient). The cost per recruited patient from a local newspaper article was 2.72 Pounds (0.2 personnel hours/patient). The cost differential between the two recruitment methods was largely owing to poor administration practices, difficulties in accessing patient information, and difficulties in contacting patients from the general practice computer database.