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In 6 experiments, it was investigated whether the pattern of warming from storage temperature to incubation temperature affects early embryonic mortality in broiler eggs. The warming profile (WP) from 21°C to the final incubation temperature of 37.8°C was divided into 2 equal parts (above and below 29.4°C) and the duration of warming in both parts was varied (3 to 17 h). In all experiments, eggs were stored for 13 to 16 d at a storage temperature of 18±2°C. In experiment 1, embryo morphology was evaluated at several time points during a linear warming curve of 24 h from 21°C to an eggshell temperature (EST) of 37.8°C. Results from experiment 1 showed that during the 24 h of warming, embryos did not advance in morphological stage (P = 0.74). Results of experiment 2 and 3 showed that the duration of the WP below 29.4°C (3 to 17 h) had no effect on early embryonic mortality (P ≥ 0.77). Experiment 4 and 6 showed that in eggs from prime breeders, a slow WP (>12 h) above 29.4°C resulted in lower embryonic mortality during the first 2 d of incubation (on average 5.0%) compared to a fast WP of 3 to 6 h (on average 11.3%). In experiment 6, an interaction was found between WP and breeder flock age for embryonic mortality till day 7 of incubation (P = 0.002). Warming profile did not affect embryonic mortality during the first 7 d of incubation in eggs from the young breeder flock. However, in eggs from the prime breeder flock, a WP of 12 h in the first part of warming, followed by 17 h in the second part of warming (WP12-17) had 6.2% lower embryonic mortality in the first 7 d of incubation compared to WP12-3. It can be concluded that a slower WP above 29.4°C reduces early embryonic mortality in long stored eggs, especially those of prime breeder flocks. At this moment, it remains unclear which mechanisms are involved in this phenomenon. [ABSTRACT FROM AUTHOR]