BACKGROUND: Only limited information is available on healthy young women's perspective of their own lifestyle behaviours. By lifestyle behaviours, e.g. smoking and physical activity, individuals have the possibility to influence bone mineral density (BMD). The aim of this study was to generate a theoretical model of lifestyle behaviours among young women with different BMD changes. METHODS: Data were collected by interviewing with 11 women, and the material was analysed by means of the grounded theory. FINDINGS: Two core categories were generated: (i) the respondents' outlook on life and (ii) their life situation. The respondents' outlook on life was either 'rigid' or 'relaxed'. Respondents who had a rigid outlook on life adjusted with others and had a decreased BMD while those with a relaxed outlook on life were doing things for fun and had an increased BMD level. Life situation also consisted of two categories: 'stagnation' and 'development'. Respondents in a static life situation did not pursue any active actions while in a developing life situation, the respondents were actively striving towards a goal. Four dimensions which characterized the respondents' outlook on life in relation to their life situation emerged: subordinating and enduring with a decreased BMD level or compromising and discerning with an increased BMD level. CONCLUSION: It seems as if the outlook on life has a greater influence than the acted lifestyle behaviour for bone development. Further research is needed to generalize the findings of this study and to explore the importance of the outlook on life among women of all ages.