Background. Low-dose treatment with acetylsalicylic acid (ASA) is widely recommended to type 2 diabetic patients as primary prevention against cardiovascular disease. High-dose treatment with cyclooxygenase inhibitors reduces urinary albumin excretion rate (AER) in type 1 diabetic patients with micro- or macroalbuminuria. Whether a similar effect on AER exists during low-dose ASA treatment, which may confound the diagnosis and monitoring of micro- and macroalbuminuria in type 2 diabetic patients, remains to be elucidated. Methods. In a randomized, double-blind, crossover trial, 31 type 2 diabetic patients with elevated levels of AER (> 30 mg/24 h) were, in random order, given ASA (150 mg/day) for 4 weeks followed by placebo for 4 weeks with a 2 week washout period or vice versa. At the end of each treatment period AER, glomerular filtration rate (GFR), blood pressure (BP), transcapillary escape rate (TERalb) of albumin and haemoglobin A1c (HbA1c) were measured. Results. The following variables remained unchanged (mean (95% CI) unless otherwise noted) (ASA vs placebo, paired Student's t-test): AER (201 (119-341) vs 205 (124-340) mg/24 h (geometric mean, 95% CI); P=0.78), GFR (103 (94-111) vs 102 (93-110) ml/min; P=0.58), systolic BP (151 (146-158) vs 152 (146-158) mmHg; P=0.68), diastolic BP (87 (83-91) vs 87 (82-91) mmHg; P=0.88), TERalb (6.3 (5.7-6.9) vs 5.9 (5.1-6.7); P=0.45) and HbA1c (8.6 (8.1-9.0) vs 8.5 (8.1-9.0)%; P=0.60). Conclusions. Low-dose treatment with 150 mg ASA daily does not have any impact on AER or GFR in type 2 diabetic patients with micro- or macroalbuminuria. Consequently, the widely recommended prescription of low-dose ASA as a primary and secondary prevention strategy against cardiovascular disease in these patients does not confound the diagnosis or monitoring of micro- or macroalbuminuria.