The NHS Health Check (NHS HC) is a cardiovascular risk assessment to prevent cardiovascular disease. Public Health England (PHE) wants to increase uptake.We explored the impact of behaviourally informed invitation letters and pre-notification and reminder SMS on uptake of NHS HCs. Patients at 28 General Practices in the London Borough of Southwark who were eligible to receive an NHS HC between 1st November 2013 and 31st December 2014 were included. A double-blind randomised controlled trial with a mixed 2 (pre-notification SMS - yes or no) × 4 (letter - national template control, open-ended, time-limited, social norm) × 2 (reminder SMS - yes or no) factorial design was used. The open-ended letter used simplification, behavioural instruction and a personalised planning prompt for patients to record the date and time of their NHS HC. The time-limited letter was similar but stated the NHS HC was due in a named forthcoming month. The social norms letter was similar to the open-ended letter but included a descriptive social norms message and testimonials from local residents and no planning prompt. The outcome measure was attendance at an NHS HC.Data for 12, 244 invites were analysed. Uptake increased in almost all letter and SMS combinations compared to the control letter without SMS (Uptake 18%), with increases of up to 12 percentage points for the time-limited letter with pre-notification and reminder (Uptake 30%; Adjusted Odds Ratio AOR 1.86; 95% CI 1.45-2.83; p < 0.00); 10 percentage points for the open-ended letter with reminder (Uptake 27%; AOR 1.68; 95% CI 1.31-2.17; p < 0.00) and a 9 percentage point increase using the time-limited letter with reminder (Uptake 27%; AOR 1.61; 95% CI 1.25-2.10; p < 0.00). The reminder SMS increased uptake for all intervention letters. The pre-notification did not add to this effect.This large randomised controlled trial adds support to the evidence that small, low cost behaviourally informed changes to letter-based invitations can increase uptake of NHS HCs. It also provides novel evidence on the effect of SMS reminders and pre-notification on NHS HC attendance.Retrospectively Registered (24/01/2014) ISRCTN36027094 .