The seasonal variance of suicides and attempted suicides in Italy from 1974 to 1994 has been studied to determine the extent and the nature of the seasonal influence on suicidal behaviour. The relationship between some climatic factors and suicide and attempted suicide rates has also been analyzed. A significant effect of seasonal change on suicidal behavior, with a clear peak in spring has been detected (ANOVA: df = 3/248, F = 5.875, p = 0.0007 for suicide; df = 3/248, F = 6.198, p = 0.0004 for attempted suicide), with a greater seasonal effect on males than females. The monthly distribution of suicide deaths and of attempted suicides follows a significant direct relationship with exposure to sun, and an inverse relationship with rainfall levels. So, one of the possible explanations for the effect of seasonal change on suicidal behaviour could be the changing seasonal climate. The complex influence of seasonal climate on human biological rhythms, particularly on 5-HT (serotonin) related functions, together with its effects on sociorelational habits, should be considered for suicide prevention.