Background: The Magpie Trial compared magnesium sulfate with placebo for women with preeclampsia. The objective of this study was to explore women's views and experiences of participating in the Magpie Trial in the United Kingdom. Methods: Postal questionnaires were sent to 771 women participants in the Magpie Trial to assess long-term health of UK women and children. The questionnaire included three questions exploring women's experience of participating in the trial: (a) If time suddenly went backward, and you had to do it all over again, would you agree to participate in the Magpie Trial? (b) Please tell us if there was anything about the Magpie Trial that you think could have been done better; and (c) Please tell us if there was anything about the Magpie Trial, or your experience of joining the trial, that you think was particularly good. Results: Overall, 619 of the 771 women who were sent questionnaires returned them. In response to the three questions: (a) 58 percent (356) of women responded “definitely yes,” 27 percent (169) “probably yes,” 4 percent (23) “probably no,” 5 percent (33) “definitely no,” and 5 percent (34) “not sure.” No clear evidence was shown of a relationship with allocated treatment, although women who responded “probably or definitely no” were more likely to have had side effects from trial treatment. (b) Although 44 percent of women stated that nothing could have been done better, free text suggestions related to content of recruitment information, and its timing, and wanting to know treatment allocation and trial results. c) Women were generally extremely positive about being followed up and receiving trial results. Conclusions: Women were largely positive about participation in the trial and its follow-up, but still reported ways they believed the study could have been improved, such as more information, given earlier, which also has implications for clinical care.