This study was a randomised control trial with a waiting control group. It was designed to evaluate the effectiveness of a 6-month, group-based diabetes prevention programme, The Healthy Living Course and assess whether participation in the programme led to changes in modifiable risk factors for type 2 diabetes among an already at-risk pre-diabetic population. Individuals designated at risk for diabetes by their general practitioners (GPs) were screened using an Oral Glucose Tolerance Test. Volunteers (N = 307) with pre-diabetes were assigned to an intervention or wait-control group in the ratio of approximately 2 : 1. The sample was pre-tested on biochemical, anthropometric and self-report behavioural, cognitive and mood variables and post-tested either at the end of the educational/support-based lifestyle programme or the end of the wait period. The intervention group significantly improved their diabetes knowledge, motivation to change, positive affect, healthy eating and activity levels and showed significantly greater reductions in weight, body mass index, waist circumference, diastolic blood pressure and fasting plasma glucose in comparison with controls. The intervention group also changed their diagnostic status from pre-diabetes to non-diabetes at a greater rate than the wait group (43% vs. 26%) who received standard care from their GPs.