Background: We aimed to assess the point prevalence of microalbuminuria (MAU) in a sample of unselected consecutive primary-care attendees, with particular focus on patients with diabetes mellitus (with and without additional concomitant diseases) and those with hypertension. Design: Cross-sectional observational study in a nationwide representative sample of 1912 primary-care practices and a patient population consisting of 39 125 primary-care attendees. Diagnoses for diabetes, hypertension and co-morbidities were provided by the treating physician and complemented by blood pressure (BP) measurements and selected lab tests. Screening for microalbuminuria (>20 and <200 μg/ml) was done with a spot urine dipstick test. Results: The clinical diagnosis of nephropathy was assigned to 7.6% of patients. The point prevalence of MAU was 19.0% in the total sample; the proportion was 33.6% in diabetics whereas the diagnosis was assigned to only 7.1% in the total sample. Amongst diabetic patients with MAU, 92.6% had BP above the target value of < 130/80 mmHg. Frequency rates rose with increasing BP (e.g. 20.6% in diabetic patients with BP< 120/70 mmHg, and 36.3% in diabetic patients with BP > 140/90 mmHg). Of note, patients with MAU had a higher burden of co-morbidity compared to those without MAU. Conclusions: We found a high prevalence of MAU in primary care, particularly in diabetic patients. The frequency of MAU was closely related to the BP level and the degree of co-morbidity. The present study underlines the magnitude of the problem of MAU in primary care, and should serve as a starting point to initiate measures to address this important public health issue.