An epidemiologic study was conducted from 1979 through 1984 on subjects presenting transitory ischemic attacks (TIA) and admitted into our Institute. We investigated year, season, month, day, and hour of every attack on 80 patients aged between 51 and 88 years. Time-series analysis showed a seasonal pattern of disease onset in early spring. Peaks occurred in March-April, and isolated peaks were also detected in January and October. Concerning TIA-onset day, we observed a peak distribution in the last 10 days of the month. Data on the hour of onset, according to single cosinor (mesor +/- SE = 2.67 + 1.13; amplitude +/- SE = 2.57 + 1.13), yielded a significant (P less than 0.05) acrophase. The acrophase is at -135 degrees (-93 degrees, -245 degrees) for tau = 48 hr
