AIMS:To determine the long-term effectiveness of an individually tailored text-message diabetes self-management support programme, SMS4BG, on glycaemic control at 2 years in adults with diabetes with an HbA1c concentration > 64 mmol/mol (8%). METHODS:We conducted a 2-year follow-up of a two-arm, parallel, randomized controlled trial across health services in New Zealand. Participants were English-speaking adults with type 1 or 2 diabetes and with an HbA1c >64 mmol/mol (8%). In the main trial participants randomized to the intervention group (N=183) received up to 9 months of an automated tailored text-message programme in addition to usual care. Participants in the control group (N=183) received usual care for 9 months. In this follow-up study, 293 (80%) of 366 randomized participants in the main trial were included. The primary outcome measure was change in glycaemic control (HbA1c ) from baseline to 2 years. Mixed-effect models were used to compare the group differences at 3, 6, 9 and 24 months, adjusted for baseline HbA1c and stratification factors (health district category, diabetes type and ethnicity). RESULTS:The decrease in HbA1c at 2 years was significantly greater in the intervention group [mean (sd) -10 (18) mmol/mol or -0.9 (1.6)%] compared with the control group [mean (sd) -1 (20) mmol/mol or -0.1 (1.8)%], with an adjusted mean difference of -9 mmol/mol (95% CI -14, -5) or -0.8% (95% CI -1.2, -0.4; P<0.0001). CONCLUSIONS:Improvements in glycaemic control resulting from a text-message diabetes self-management support programme were sustained at 2 years after randomization. These findings support the implementation of SMS4BG in current practice.