The weekend effect—worse outcomes for patients admitted on weekends compared to weekdays—has been demonstrated in studies of several common conditions requiring hospital care. The mechanism for this effect remains undefined. This study of acute stroke admissions in the United Kingdom identifies several aspects of temporal variation in care quality. These included diurnal pattern (variation by the time of day at which patients were admitted) and a day of the week pattern (variation by the day on which patients were admitted, independent of weekend versus weekday). The results of this study indicate that the notion of a weekend effect may be an oversimplification.