A major earthquake struck the Niigata Prefecture, Japan, on October 23, 2004. This study investigated the effect of the earthquake on morning home blood pressure (MHBP) measurements, as well as clinic blood pressure (CBP) and associated complications, in 222 type 2 diabetic patients who measured MHBP and CBP before the earthquake. Physical and laboratory examinations were assessed at every three months. Each patient completed a questionnaire on MHBP measurement, Japanese intensity grade (JIS), patient's lifestyle and psychological impact using posttraumatic stress disorder (PTSD) symptom score. Median JIS showed all patients lived in areas affected by strong aftershocks. Most patients stayed in their own houses, while one-third of patients sought refuge in other houses. No new clinical manifestations of disease were noted. Median PTSD score was low. Patients in public refuge houses had daytime blood pressure, but MHBP was not measured. In the first month, the number of patients who continued MHBP measurements decreased to 27% of pre-shock level. Many patients were unable to measure MHBP for several reasons, including losing MHBP equipment, having equipment destroyed, or suffering from anxiety due to the extensive devastation. Mean systolic MHBP and median urinary albumin excretion rate (UAER) increased significantly within three months and returned to pre-earthquake level at six months. On multiple regression analysis, increased systolic and diastolic MHBPs were significantly associated with UAER elevation. In type 2 diabetic patients following an earthquake, it is important to develop a device of MHBP measurement for maintaining control of MHBP to prevent vascular complications.