Objective: To assess the effectiveness of self monitoring blood glucose levels in people with non-insulin treated type 2 diabetes compared with clinical management without self monitoring, and to explore the effects in specific patient groups. Design: Meta-analysis based on individual participant data. Data sources: Medline, Embase, and a recent systematic review of trialson self monitoring of blood glucose. Chief investigators of trials published since 2000 were approached for additional information and individual patient data. Inclusion criteria: Randomised controlled trials in patients with non-insulin treated type 2 diabetes comparing an intervention using self monitoring of blood glucose with clinical management not using self monitoring. Trials published from 2000 with at least 80 participants were included. Data collection: Individual patient data were collected from electronic files and checked for integrity. Analysis: All randomised participants were analysed using the intention to treat principle. A random effects model of complete cases was used to assess efficacy, a sensitivity analysis comprised imputed data, and prespecified subgroup analyses were carried out for age, sex, previous use of self monitoring, duration of diabetes, and levels of glycated haemoglobin (HbA 1c) at baseline. Results: 2552 patients were randomised in the six included trials. A mean reduction in HbA 1c level of -2.7 mmol/mol (95% confidence interval -3.9 to -1.6; 0.25%) was observed for those using self monitoring of blood glucose levels compared with no self monitoring at six months. The mean reduction in HbA1c level between groups was 2.0 mmol/mol (3.2 to 0.8; 0.25%) at three months (five trials) and 2.5 mmol/mol (4.1 to 0.9; 0.35%) at 12 months (three trials). These estimates were unchanged after imputing missing data, and estimates of effect in trials with higher loss to follow-up or a possibility of co-intervention compared with those with lower loss to follow-up and no co-intervention did not differ significantly (P=0.21). The difference in HbA 1c levels between groups was consistent across age, baseline HbA 1c level, sex, and duration of diabetes, although the numbers of older and younger people and those with HbA 1c levels >86 mmol/mol (10%) were insufficient for interpretation. No changes occurred in systolic blood pressure (-0.2 mm Hg, 95% confidence interval -1.4 to 1.0), diastolic blood pressure (-0.1 mm Hg, -0.9 to 0.6), or total cholesterol level (-0.1 mol/L, 95% confidence interval -0.2 to 0.1). Conclusions: Evidence from this meta-analysis of individual patient data was not convincing for a clinically meaningful effect of clinical management of non-insulin treated type 2 diabetes by self monitoring of blood glucose levels compared with management without self monitoring, although the difference in HbA 1c level between groups was statistically significant. The difference in levels was consistent across subgroups defined by personal and clinical characteristics.