OBJECTIVE:Masked (MUCH) and white coat uncontrolled hypertension (WUCH) are more and more frequently investigated for their long-term prognostic significance Classification is usually made by a single set of office and out-of-office blood pressure (BP) measurements during the treatment period. To evaluate the long-term reproducibility of MUCH and WUCH, an information crucial for determining the long-term prognostic impact of these conditions. DESIGN AND METHOD:Reproducibility of MUCH and WUCH was assessed in 1664 hypertensive patients recruited for the ELSA study treated with atenolol or lacidipine (+/– additional drugs) during a 4-year period. Office and 24-hour BP was measured at baseline and every year during treatment, allowing repeated classification of either condition. RESULTS:After 1 year of treatment 21.1% and 17.8% of the patients were classified as MUCH and WUCH, respectively. For both conditions the prevalence was similar in the following years, although with a large change in patients composition because only about 1/3 of patients classified as MUCH or WUCH at one set of office and ambulatory BP measurements maintained the same classification at a subsequent set of measurements. In only 4.5% and 6.2% MUCH and WUCH persisted throughout the treatment period. MUCH and WUCH reproducibility was worse than that of patients showing control or lack of control of both office and ambulatory BP. CONCLUSIONS:Both MUCH and WUCH display a poor reproducibility over time. This should be taken into account in studies assessing the long-term prognostic value of these conditions based on only one set of BP measurements.