OBJECTIVE: Aside from diminished daily functional capacity, individuals with depression are at greatly higher risk of suicide. Given that both endogenous depression severity and the incidence of suicide peak during the spring and summer months, it would seem that an environmental cue—one that generates alterations in brain neuronal activity that result in depressed affect or suicidal ideation—might be important. METHOD: The authors examined the frequency of suicide and its relation to meteorological factors in the state of Victoria between January 1990 and April 1999. RESULTS: The incidence of suicide had its nadir in winter and zenith in the spring and summer and paralleled closely the number of bright sunlight hours. This pattern was particularly marked for violent suicide. During the decade, the suicide rate significantly increased among men between 21 and 60 years of age and women between 41 and 60. CONCLUSIONS: The incidence of suicide in southeastern Australia displays a clear seasonal pattern, being positively linked with prevailing levels of sunlight. The rate of suicide increased in the latter half of the last decade.