The secular weight increase in European and US adolescents and the increasing use of oscillometric devices pose a problem to decide on normative blood pressure levels. We studied how biological and statistical aspects influence standards, and suggest new Northern Europe reference tables. All adolescents of Nord-Trøndelag county, Norway, aged 13-18 years were invited to the Nord-Trøndelag Health Study II (1995-1997), and the participation rate was 90% (n = 7682 after excluding 278 chronically ill patients). Blood pressure was measured with an oscillometric device (Criticare 507N, Criticare Systems Inc., Waukesha, Wisconsin, USA). We found that overweight introduced a systematic bias in blood pressure results (+3-5 mmHg). In addition to the well known differences with age and sex, we found evident 95th percentile differences in systolic blood pressure between the tallest and shortest individuals, ranging from 3-17 mmHg, and postpubertal status increased systolic blood pressure by 2-4 mmHg. We also found that a polynomial regression model with ln(blood pressure) as the dependent variable better accounted for the higher variation in blood pressure in subgroups with higher mean blood pressure. The suggested reference tables have a similar 50th percentile to British oscillometric data (1-4 mmHg above), whereas our 95th percentiles were 4-7 mmHg above. Compared with US sphygmomanometric data, our values range 5-12 and 10-16 mmHg above, respectively. We conclude that all blood pressure reference tables for adolescents should be region specific and based on normal-weight individuals. In addition to age and sex, height, puberty, type of measurement device and different variances in different age groups should also be accounted for.