To study physical activity among Icelandic adults and the relationship with anthropometric factors and grip strength.Randomly selected participants, 30-85 years of age, answered questions regarding exercise and diet. Body composition was measured with DXA, which detects the proportions of different body tissues. Height, weight and grip strength were measured and the body mass index (kg/m(2)) was calculated. The prevalence of regular physical activity was studied for men and women in the age groups of 30-45 years, 50-65 years and 70-85 years and the relationship to body mass index, body composition and grip strength examined. The possible preventive effect of exercise on overweight and obesity was also studied.Of 2310 invited, 1630 subjects (70.6%) participated. Mean participation in regular physical activity was 3-4 times a week but 19% of the women and 24% of the men did no exercise at all. In general, swimming, walking and calisthenics of various types and intensities were the most common forms of exercise and in the age group 30-45 year old 16% of the women and 8% of the men did strength training. 50.4% of women 30-45 years of age and 68.2% of 50-65 year old men were overweight or obese. Mean fat mass was highest in 70-85 year old women (38%) and men (27%). Occupational activity was not related to body mass index, body composition or grip strength. Significant negative relationship was found between frequency of exercise and fat mass. The relationship between grip strength and lean mass or exercise was non-significant. The odds ratio of being overweight or obesity was 0.5 (CI was 0.37-0.77 for women and 0.37-0.94 for men) for those who exercised five or more days per week compared to those who exercised less frequently.One of four Icelandic men and one of five women do not participate in regular physical activity despite of strong scientific indications of various positive health effects of exercise. More than half of adult Icelanders are overweight or obese but the risk is halved among those who exercise at least five days per week, compared to those who exercise less frequently. Sedentary lifestyle is more common amongst Icelanders than in the neighboring countries and realistic goals need to be set to increase the participation in regular physical activity.