BACKGROUND AND AIM: In most parts of the western world, screening routines for gestational diabetes mellitus (GDM) are implemented, however, knowledge of the impact GDM has on the experience of pregnancy and life situation is sparse. The aim of this study was to describe pregnant women's experiences of acquiring and living with GDM during pregnancy. METHOD: A Grounded Theory approach was used. Ten pregnant women diagnosed with GDM in current pregnancy were interviewed. Data collection was performed in the north of Sweden over two periods; a first set of interviews in 1998-2000 and additional interviews in 2006 to further explore the experience and reach saturation. FINDINGS: 'From stun to gradual balance' emerged as the core category, encompassing of the categories 'Struck by lightning', 'Having a personal responsibility', 'Being under surveillance', 'Struggling for protection', 'Feeling socially apart', 'Being sufficiently supported', 'Changing the self-image', 'Adapting to a new situation' and 'Waiting for the 'Moment of truth''. Our findings indicated that the diagnosis of GDM initiated a number of challenges and demands for the pregnant women. Further, being diagnosed with GDM was not only perceived as a medical complication threatening the pregnancy, moreover as an indicator of a future diabetes mellitus. CONCLUSION: The experience of being diagnosed with and living with GDM during pregnancy may be understood as a process 'from stun to gradual balance'. The experience comprises positive and negative dimensions. Despite the challenges, the inconveniences and the changes involved, gradually adapting to a lifestyle and balancing the every day life is the prize most of these women are willing to pay in order to secure optimal maternal and foetal health. Knowledge of the experiences of women diagnosed with GDM may enable midwives to provide increased support as well as provide information and preventive measures in order to delay future diabetes mellitus.