Objective. To examine in previously sedentary older women the effects of exercise mode and a behavioural intervention on short and long-term retention and adherence.Methods. Healthy, sedentary women aged 50-70 years (N= 116) were randomly assigned to a supervised 6-month swimming or walking program 3 sessions a week. They were further randomised to usual care or a behavioural intervention. The same program was further continued unsupervised for 6 months. We assessed retention, adherence, stage of exercise behaviour and changes in fitness.Results. One hundred women (86%) completed 6 months and 86 (74%) continued for 12 months. Retention rates were similar for both exercise modes at 6 and 12 months. Adherence to swimming or walking was similar after 6 months (76.3 (95% Cl: 69.5, 83.1)% vs. 74.3 (67.7, 80.9)%) and 12 months (65.8 (57.9, 73.8)% vs. 62.2 (54.6, 70.0)%). The behavioural intervention did not enhance retention or adherence. Fitness improved for both exercise modes after 6 months and was maintained at 12 months.Conclusions. Either swimming or walking programs initiated with careful super-vision over 6 months resulted in similar high retention and adherence rates by highly motivated older women over 12 months. Behavioural intervention in this setting did not improve these rates further. (C) 2008 Elsevier Inc. All rights reserved.