Data on self inflicted injuries by poisoning in the Winnipeg, Canada area were compared to the lunar cycle. A statistically significant lunar periodicity was demonstrated for the females in the sample (p<.05) with a greater number of cases occurring during the first quarter and a smaller number occurring during the third quarter of the lunar cycle. The males did not show a lunar periodicity and showed a significantly different distribution than the females in the sample (p<.025). A significant correlation between periods in which a large number of self inflicted injuries occurred and the apogees and perigees of the moon, was found (p<.005). The possibility that factors such as weather with its accompanying electromagnetic processes and/or changes in the intensity of the geomagnetic field are mediating factors in a lunar phase effect on human behavior, is discussed.