We assessed the OSCILL-IT ambulatory blood pressure (BP) recorder (FIGI sr1, Rome, Italy) according to the performance criteria set out by the British Hypertension Society (BHS) protocol. The OSCILL-IT is a portable, noninvasive recorder that uses a process that correlates systolic, mean, and diastolic areas, identified on the oscillations, to the cuff absolute pressure. According to the recommendations of BHS, a large heterogeneous population (100 subjects: 52 men aged from 19 to 79--median 44 and 48 women from 19 to 74--median 54) was recruited in order to assess accuracy and to analyze, in addition, the effects of observer agreement and BP level on the observer-device differences. With reference to BP level, we suggest also a new graphic approach. Four sets of sequential, same arm, comparative BP measurements were obtained, performed by the OSCILL-IT recorder and two skilled clinicians using a mercury column, for each subject. We used a linear combination for the statistical evaluations. We confirmed the observer agreement through the frequency distribution of BP as a function of the observer and through the differences between observers. We compared OSCILL-IT with sphygmomanometric readings: the differences were not significant. A visual inspection, with the addition of regression lines, showed that there were no variations in differences at the changing of BP level. The difference between observers and OSCILL-IT was 0.2 +/- 5.3 mm Hg and 0.2 +/- 5.8 mm Hg both for systolic BP (SBP) and diastolic BP (DBP). The level of agreement, according to BHS criteria, showed that 64% of all systolic and 70% of all diastolic readings obtained by the OSCILL-IT were within 5 mm Hg of the sphygmomanometric determinations. Therefore, the grade is C for SBP, even if 93% of SBP and 95% of DBP obtained by the OSCILL-IT were within 10 mm Hg of the sphygmomanometric determinations. These analyses demonstrate that the OSCILL-IT satisfies the accuracy parameters and the additional linear regression yields graphics more immediate.