Large disruptions of chronobiological rhythms are documented as destabilizing individuals with bipolar disorder; however, the impact of small phase altering events is unclear. Australian suicide data from 1971 to 2001 were assessed to determine the impact on the number of suicides of a 1-h time shift due to daylight saving. The results confirm that male suicide rates rise in the weeks following the commencement of daylight saving, compared to the weeks following the return to eastern standard time and for the rest of the year. After adjusting for the season, prior to 1986 suicide rates in the weeks following the end of daylight saving remained significantly increased compared to the rest of autumn. This study suggests that small changes in chronobiological rhythms are potentially destabilizing in vulnerable individuals.