QUESTIONS: What are the attitudes of women diagnosed with gestational diabetes mellitus (GDM) towards physical activity during pregnancy? What are the perceived barriers to and enablers of physical activity during pregnancy in women with GDM? DESIGN: A qualitative study with phenomenology and interpretative description as theoretical frameworks. PARTICIPANTS: Pregnant women experiencing an uncomplicated singleton pregnancy, diagnosed with GDM, and aged 18 to 40 years were recruited using purposive sampling. METHOD: Semi-structured interviews were recorded, transcribed verbatim and returned to participants for member checking. Three researchers independently and thematically analysed the qualitative data using an inductive method. Data were coded and compared, and themes were developed, discussed and defined. Recruitment continued until data saturation. Emergent themes were sent to participants and peer reviewed for confirmation. RESULTS: The participants were 27 women, with mean age 32 years (SD 3), mean gestation 30 weeks (SD 5), mean pre-pregnancy body mass index 26 kg/m (SD 5), and born in 10 different countries. The process of communicating information about physical activity (messaging) was the main theme to emerge. Sub-themes included: wanting information about physical activity from credible sources; wanting clear, specific information about safe physical activity during a GDM pregnancy; receiving information at GDM diagnosis because this event triggered women's desire to be more physically active; understanding why physical activity is important to improving outcomes for themselves and their babies; and wanting information about flexible, convenient and practical physical activity options. CONCLUSION: To feel confident and safe about being physically active during pregnancy, women with GDM wanted clear, simple and GDM-specific messages from credible sources. Health professionals can support women with a GDM pregnancy with targeted physical activity messages.