OBJECTIVES: Patients with T2DM have an increased risk of comorbidities associated with weight gain. Depending on patients’ weight, treatment guidelines give preference to treatments that have favourable weight profiles, with weight gain being an important adverse event to avoid. This study aims to characterize baseline characteristics, weight and glycaemic change in patients prescribed new antidiabetic treatment.     METHODS: Patients with T2DM diagnosis and receiving first new antidiabetic treatment class (index) between 01/01/05-01/01/12 were identified in UK CPRD primary care records. Index class could be first-line, switch or add-on. Demographics, baseline weight and glycosylated haemoglobin (HbA1c), and change at 6 months were described by index class.   RESULTS: Of 23,987 included (of whom 133 were lost to follow-up) 64.7% initiated metformin (MET), 15.5% sulfonylureas (SU), (14.0%) thiazolidinediones (TZD), 2.1% dipeptidyl-peptidase-4-inhibitors (DPP4), 1.9% insulin, 0.7% glucagon-like-peptide-1-agonists (GLP-1), 0.6% ‘other’, 0.5% acarbose. About 57% were men; baseline mean age for different index classes ranged between 56.5 (insulin) and 63.1 years (acarbose). Mean baseline weight ranged between 88.0 (SU) and 112.4 kg (GLP-1) and mean baseline HbA1c between 72.6 mmol/mol (8.8%) (acarbose) and 84.7 mmol/mol (9.9%) (insulin). Among 14,438 patients with six-month follow-up data an increase in weight was found for subjects initiating SU (2.1%;95%CI: 1.9;2.4,n=2,223), TZD (1.9%;95%CI: 1.7;2.1,n=2,034) and insulin (1.8% ;95%CI: 1.0;2.6,n=285). A reduction in weight was observed for patients on GLP-1 (-3.4%;95%CI: -4.3;-2.5,n=119), DPP4 (-0.9%;95%CI: -1.4;-0.4,n=347) and MET (-0.8%;95%CI: -0.9;-0.7,n=9,278). A mean reduction in HbA1c over the six month period was seen for all antidiabetic classes but was not statistical significant for GLP-1 and ‘other’. CONCLUSIONS: These results indicate that initiation of antidiabetic agents such as SU, TZD and insulin frequently are associated with weight gain. This underscores the need to choose agents with favourable weight profiles for overweight or obese patients, as recommended by UK T2DM treatment guidelines.