Obesity and type 2 diabetes are inextricably linked. It is therefore unfortunate that insulin, the ultimate treatment to improve glycaemic control in type 2 diabetes, is associated with significant weight gain. The aim of the present investigation was to ascertain whether a dietitian-led intensive lifestyle intervention could attenuate weight gain associated with commencing insulin therapy. Subjects (n 50) with type 2 diabetes, within 4 weeks of starting insulin therapy, were randomly allocated to a control or intervention group. The control group continued with standard care whilst the intervention group followed a dietitian-led intensive lifestyle intervention. Over 6 months the control group gained 4.9 (sd 3.6) kg (P < 0.001), whilst the intervention group maintained their weight ( - 0.6 (sd 5.1) kg (NS). The difference in weight change between the groups was 5.5 kg (P < 0.001). The control group had significant increases whilst the intervention group had slight decreases in: BMI (+1.7 (sd 1.3) kg/m2 (P < 0.001) v. - 0.3 (sd 2.0) kg/m2 (NS)), waist circumference (+5.3 (sd 5.0) cm (P < 0.001) v. - 0.4 (sd 5.2) cm (NS)) and percentage body fat (+1.5 (sd 2.0) % (P < 0.001) v. - 0.4 (sd 2.8) % (NS)). Differences between the groups for these parameters were significant (P < 0.01). Throughout the study, both groups experienced significant reductions in HbA1c, but only minor changes in blood lipids. The present study demonstrates that weight gain is not an inevitable consequence of starting insulin therapy, but attenuation of the weight gain requires a high level of intervention. The first 6 months to 1 year after initiating insulin therapy provides the ideal 'window of opportunity'.