The aim of this study was to describe the underlying theory and the implementation of a 2-year individualized physical activity counseling intervention and to evaluate whether benefits persisted 1.5 years after the intervention. The sample included 632 sedentary 75- to 81-year-old participants. Data were collected in 2003-2005. The participants were randomly assigned to an intervention group and a control group. The intervention consisted of an individualized face-to-face meeting followed by telephone contacts every 4 months for 2 years, with the aim to increase participation in specific physical activities as well as to increase habitual physical activity. At the 2-year follow-up, the prevalence of physical activities in the intervention group vs. control group was as follows: supervised calisthenics training 20 vs. 16%, walking for fitness 69 vs. 62%, weight training 13 vs. 8% and water aerobics 19 vs. 7%. For water aerobics and walking for fitness, the treatment effect was significant [water aerobics odds ratio (OR) 2.49, 95% confidence interval (CI) 1.16-5.36, walking for fitness OR 1.58, 95% CI 1.05-2.40]. As to the other activities, the effect did not reach statistical significance. At the 1.5-year post-intervention, the follow-up results indicated that the intervention effect was still evident. The subgroup analyses suggested that physical activity counseling may be most efficacious among people with intact mobility, while those having manifest mobility limitations may not benefit from it. Older people who have manifest mobility limitations may need more face-to-face counseling.