Aims: Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) prevent the progression of diabetic nephropathy (DN). Studies suggest that combination renin-angiotensin-aldosterone system (RAAS)-inhibiting therapy provides additive benefit in DN. However, these studies are small in size. We performed a meta-analysis of studies investigating combination therapy for DN. Methods: Studies were identified through a search of medline, embase, cinahl and the Cochrane Database. All trials involving combined ACEI and ARB for slowing progression of DN were included. The primary end point was 24-h urinary protein excretion. Blood pressure, serum potassium and glomerular filtration rate (GFR) were secondary end points. Results: In the 10 included trials, 156 patients received ACEI + ARB and 159 received ACEI only. Most studies were 8-12 weeks in duration. Proteinuria was reduced with ACEI + ARB (P = 0.01). This was associated with significant statistical heterogeneity (P = 0.005). ACEI + ARB was associated with a reduction in GFR [3.87 ml/min (7.32-0.42); P = 0.03] and a trend towards an increase in serum creatinine (6.86 μmol/l 95% CI -0.76-13.73; P = 0.09). Potassium was increased by 0.2 (0.08-0.32) mmol/l (P