The aim of our study was to compare ambulatory blood pressure monitoring (ABPM) measures (mean systolic/diastolic blood pressure, diurnal rhythm, and pressure burden) in matched normo- and microalbuminuric (IDDM) adolescents and healthy controls. Twenty-four hour monitoring was undertaken in 39 normotensive (normal clinic blood pressure measurements) IDDM adolescents (22 normo- and 17 microalbuminuric subjects) and 23 controls. Subjects were matched for age, bodymass index, gender, and IDDM duration. Microalbuminuria was diagnosed on the basis of a urinary albumin excretion rate greater than 15 but less than 200 micrograms/min in two of the three 24-h urine collections. The microalbuminuric patients differed from the normoalbuminuric subjects and controls in having higher mean 24-h and overnight systolic pressure, loss of systolic diurnal rhythm and increased systolic and diastolic pressure burden. There were no differences between the three groups in diastolic blood pressure. The normoalbuminuric group differed from the controls only with respect to an increased systolic pressure burden. Microalbuminuric IDDM adolescents show similar, albeit milder changes in ABPM, to those reported in adults with microalbuminuria. We postulate that these milder changes represent an earlier phase to that observed in the adult population and that taken together, the adolescent and adult data suggests a specific order in the development of ABPM changes in diabetic subjects.