To clarify psychological factors related to white coat hypertension, we examined personality characteristics of patients with mild essential hypertension by psychological testing. Patients with essential hypertension were taught to measure their own blood pressure (BP) with a semi-automatic oscillometric BP measuring device and were asked to measure BP at home in the sitting position before going to sleep. The duration of the study was 8 wk. Patients were defined as "white coat" hypertensive patients (WCHT) (n = 49) if home systolic BP was 135 mmHg or less and home diastolic BP was 85 mmHg or less, and as "sustained" hypertensive patients (SHT) (n = 53) if home systolic BP was 140 mmHg or more or home diastolic BP was 90 mmHg or more. All the patients underwent the following psychometric tests: self-rating questionnaire for depression, MMPI alexithymia scale, type A behavior pattern check list, general health questionnaire (GHQ), and egogram check list. WCHT did not differ from SHT in the scores for depression, alexithymia, type A behavior pattern, or GHQ. However, WCHT showed an abnormal pattern on egograms, as compared with SHT. On egograms, SHT showed a normal hill-shaped pattern with a peak in "nurturing parent (NP)", and "free child (FC)" was higher than "adapted child (AC)" in both genders. In contrast, WCHT showed significantly lower FC and significantly higher AC than SHT, and AC was higher than FC in both genders. These findings suggested that WCHT tend to suppress their own emotions and become over-adaptive to their surroundings, as compared with SHT.