Aim of the Study. To characterize suicide seasonality in the Odessa region, to estimate the relation of this phenomenon to day length and ambient temperature. Methods. The research is based on the analysis of 11220 cases of completed suicides in the city of Odessa and Odessa region in 2000-2016. Initial data are presented by the Odessa Regional Forensic Bureau. All data were processed statistically, previously being reduced to a single scale, taking into account the different number of days in the months of the year. To study the statistical hypothesis about the equality of the proportions of suicides per month of the year, a binomial criterion with a two-sided critical region was used. Results. Suicides in Odessa region grow from March to August, the maximum is seen in May-June, while the minimum can be observed in December-February. Seasonality pattern in Odessa region is rather strongly marked. Thus, an average number of suicides in May for 58% exceeds that in December. The autumn peak (in October) is less pronounced and unstable. Recently two main pathophysiological hypotheses are proposed as an explanation of a phenomenon of the seasonality of suicidal behavior - about a role of a light and temperature factor. For the purpose of identification of differential influence of these factors correlation and the graphic coincidence of curves of suicides, longitudes of day and of a temperature within a year were estimated. An extremely high correlation between the daylight hours and the frequency of suicides was found (linear correlation coefficient r=0,97, significance value 1,3 10-7). It was also found that suicides are closest to average during the year (expected from the point of view of a hypothesis) in March and September, i.e. around spring and autumn equinox. In all other months of the year, when the length of the day is less, the proportion of suicides is significantly less than expected; on the contrary, longer day hours are associated with higher than expected frequency of suicide. At the same time, an association with the temperature factor is also observed, and to a greater extent with the derivative of the monthly temperature, which reflects the rapidity of the change. More precisely, the derivative of the monthly temperature curve is shifted one month forward from suicides curve, which may be attributed to the provocative role of the temperature factor. Conclusion. The obtained data support the role of both factors and the imply the presence in the population of suicide completers two certain subpopulations, whose self-aggressive behavior is mainly dependent on the day length (which implies the role of serotonin/melatonin dynamics) or the ambient temperature (which implies the role of neural and humoral mechanisms of thermoadaptation). To confirm this hypothesis more studies are needed in the regions with a bigger contrast of summer and winter temperatures and in more northern and southern latitudes differing in the insolation pattern.Seasonal variations in the number of suicides in Odessa and the Odessa region for the period 2000-2016 are analyzed. All data were processed statistically, previously being reduced to a single scale, taking into account the different number of days in the months of the year. Suicides in the Odessa region grow from March to August, the maximum is seen in May-June. The autumn peak (in October) is less pronounced and unstable. To study the statistical hypothesis about the equality of the proportions of suicides per month of the year, a binomial criterion with a two-sided critical region was used. A high correlation between the daylight hours and the frequency of suicides was found. Suicides are minimal in March and September (spring and autumn equinox), in all other months of the year, when the length of the day is less, the proportion of suicides is significantly less than expected, on the contrary, longer day hours are associated with higher than expected frequency of suicide. At the same time, an association with the temperature factor is also observed, and to a greater extent with the derivative of the monthly temperature, which reflects the rapidity of the change. The obtained data support the role of both factors and the presence in the population suicide completers certain subpopulations whose self-aggressive behavior is mainly dependent on the day length (which implies role of serotonin/melatonin dynamics) or the ambient temperature (which implies role of neural and humoral mechanisms of thermoadaptation).