During a 6 months' period, 99 persons, randomly chosen among patients admitted for attempted suicide to the Department of Psychiatry, Odense University Hospital, were interviewed. This paper, which is the first in a series, deals with the theoretical and methodological background of the survey and the validity of the sample and also with some basic social characteristics of the suicide attempters. The majority of the suicide attempters were found to be single and many of them were living alone or alone with children. The sample could also be characterized by a low level of vocational education and by lack of association with the labour market. The suicide attempters could not, however, be unequivocally described as being in bad financial circumstances, neither were they solely from the lower social classes; the social status profile of the suicide attempters was closer to the status profile of suiciders, with relatively many persons from both upper and lower classes and few from the middle class.