The aim of the Nordic Diltiazem (NORDIL) Study was to compare cardiovascular morbidity and mortality in calcium-antagonist-based treatment with diltiazem and conventional diuretic/beta-blocker-based treatment in essential hypertension. The objective of the present sub-study was to compare self-measured home blood pressure with office blood pressure at a time-point in the study when the patients' blood pressures had been treated to the level that the investigators conceived to be the blood pressure target. The NORDIL study was prospective, randomized, open and endpoint-blinded. It enrolled 10881 patients aged 50-74 years at health centers in Norway and Sweden who had diastolic blood pressure (BP) of 100 mmHg or more. The present sub-study group (n = 87) was small but fairly representative for the entire study population regarding baseline characteristics. Both systolic (4.0 mmHg, p = 0.01) and diastolic blood pressures (3.1 mmHg, p < 0.001) were significantly lower at home than in the office. Pearson correlation coefficients between the respective office and home readings were statistically highly significant (p < 0.001), but of moderate strength ranging from r = 0.41 for heart rate to r = 0.46 and r = 0.58 for diastolic and systolic blood pressures, respectively. Altman plots also gave statistical support to some inconsistency between the two methods of measurements. Pearson correlation coefficients between afternoon and morning measurements showed strong relationships with r-values >0.9 for both blood pressures and heart rate. The Altman plots also suggested excellent consistency between afternoon and morning measurements. Thus, motivated and trained hypertensive patients can perform home recordings of blood pressure and heart rate with precision; however, there are differences between recordings at home and in the investigators' offices that suggest some degree of "white coat effect" in these treated hypertensives.