Sixty-nine percent of a random sample of 1,835 non-institutionalised elderly 70-95 year old persons in four Danish communes answered a mailed questionnaire on their health and social situation. However, 17% replied that they did not want to or could not manage to answer the questionnaire and the remaining 14% did not respond. The response rate was highest among the younger persons and lowest the age group 85-89. The response rate was higher in the metropolitan area and the rural area, lower in the urban area. The response rate was not associated with gender. In one commune, the non-respondents were approached for personal interviewing and 60% of this group were interviewed. In this commune, personal interviewing increased the response rate from 68 to 78%. Respondents to the postal questionnaire and respondents to the personal interview were compared regarding 228 variables and were shown to be alike in most respects. In the group of personally interviewed persons an overrepresentation of persons living alone and individuals with reduced social, mental and health ressources was demonstrated.