Insulin pump therapy improves glycaemic control in individuals with type 2 diabetes. However, it may be associated with weight gain. Aim: To test the effectiveness of a six-month dietary and physical activity intervention, compared to usual care, on weight gain prevention after initiation of insulin pump. Methods: Multicentre randomized, controlled trial of 54 individuals. Primary endpoint was between group difference in weight gain at six-months. Results: Weight gain after 6 months of insulin pump treatment did not differ between groups: mean 3.2 (3.9) kg in the control group and 3.9 (3.8) kg in the intervention group, (p = 0.56). HbA1c improved without difference between groups. Post-hoc multivariate analysis of all participants found that weight gain was independently associated with younger age, active smoking, and the magnitude of HbA1c reduction. A 1 % decrease in HbA1c was associated with an increase of 0.94 kg [95 % Confidence Interval 0.47; 1.41], p < 0.001. Conclusions: Treatment intensification by insulin pump therapy in patients with type 2 diabetes is effective to improve glycaemic control. A gain of about 1 kg per 1 % drop in HbA1c can be expected after insulin treatment intensification. This weight gain was not prevented by a home-base, individualized, 6-months lifestyle intervention program.