The article investigates the identity formation of the membership of a multidisciplinary scientific association, the Society of Social Medicine in Finland. The research asked whether the members of the Society had some kind of identity that refers to social medicine and what reasons did they give for having or not having this identity. The data comes from a postal questionnaire sent to all members of the Society in 1999 (N = 429, the response rate was 63 %). Identity was assessed with the question: Do you think of yourself as ‘a social medicinist’?” About half of the people who answered the questionnaire had this identity, 30 % had it clearly, and in 22 % of the cases this depended on the situation. The grounds for having the identity were examined in three groups: lacking, clear and situational. In addition, statistical analysis was used to determine explanatory factors. The reasons for having the social medicine practitioner’s identity were professional and related either to one’s own research activity or practical work. The most significant explanatory factors for a strong identity were the male sex, age less than 40 years, and medical training.