BackgroundContinuous monitoring of the mortality phenomenon is given high priority in the current recommendations for the preparation of heat action plans in Germany with respect to problem detection and evaluation of interventions. International monitoring systems are heterogeneous concerning the procedures used. In Germany, such monitoring systems are rarely established.ObjectivesUnder what circumstances can amortality monitoring system be operated on aregional basis using routine data?Materials and methodsSummer mortality data from Hesse from 2000 to 2018 and their associations with climate variables were analyzed. Different approaches regarding spatial analyses, definition of excess criteria, and adjusting procedures were explored.ResultsIn Hesse, daily mean temperatures averaged over all operating weather stations proved appropriate as a climate parameter. The expected daily number of deaths was estimated by amoving average based on 25daily mortality datasets from reference periods of five years adjusted for mortality peaks using data from three previous years. Mortality excess was defined as twice the value of the standard deviation of the expected values including an empirically determined temperature threshold. This threshold was derived from analyzing relative frequencies of observed excess number of deaths per 1? temperature interval. Based on this approach, 49mortality excesses with atotal of 889 excess deaths were estimated in Hesse during days with adaily mean temperature of more than 23.0? during summer from 2005 to 2018.ConclusionsThe system described in this article turned out to be practicable for systematically monitoring mortality during summer. Timely availability of mortality and climate data is crucial.