The objective of the reported research was to assess the impact of text message (SMS) reminders and their content on cervical screening rates. Women invited for cervical screening in Northwest London from February-October 2015 were eligible. 3133 women aged 24-29 (Study 1) were randomized (1, 1) to 'no SMS' (control), or a primary care physician (PCP) endorsed SMS (SMS-PCP). 11,405 women aged 30-64 (Study 2), were randomized (1, 1:1:1:1:1:1) to either: no SMS, an SMS without manipulation (SMS), the SMS-PCP, an SMS with a total or proportionate social norm (SMS-SNT or SMS-SNP), or an SMS with a gain-framed or loss-framed message (SMS-GF and SMS-LF). The primary outcome was participation at 18 weeks. In Study 1 participation was significantly higher in the SMS-PCP arm (31.4%) compared to control (26.4%, aOR, 1.29, 95%CI: 1.09-1·51; p = 0.002). In Study 2 participation was highest in the SMS-PCP (38.4%) and SMS (38.1%) arms compared to control (34.4%), (aOR: 1.19, 95%CI: 1.03-1.38; p = 0.02 and aOR: 1.18, 95%CI: 1.02-1.37; p = 0.03, respectively). The results demonstrate that behavioral SMSs improve cervical screening participation. The message content plays an important role in the impact of SMS. The results from this trial have already been used to designing effective policy for cervical cancer screening. The NHS Cervical Screening Programme started running a London-wide screening SMS campaign which was based on the cervical screening trial described here. According to figures published by Public Health England, after six months attendance increased by 4.8%, which is the equivalent of 13,400 more women being screened at 18 weeks.