We present an evaluation of the performance of Meteosat Lightning Imager (MTG-LI) in detecting lightning flashes. To achieve this, we applied a Bayesian relative detection efficiency (RDE) analysis using the European ground-based lightning detection network (ALDIS/BLIDS) as reference. The analysis involved pairing each ALDIS/BLIDS stroke/pulse with corresponding MTG-LI level-2 groups. Between July 2024 and January 2025, MTG-LI detected 50 to 54% of groups and 62 to 63% of flashes relative to ALDIS/BLIDS in datasets covering nationwide data (Switzerland and Austria) and dominated by downward cloud-to-ground and intracloud flashes. For context, the International Space Station Lightning Imaging Sensor, assessed with identical matching criteria, reaches only 36.5% group-level and 48.4% flash-level RDE. In regions near tall structures such as the Säntis (2502 m) and Gaisberg (1287 m) towers, where upward flashes dominate, MTG-LI demonstrated significantly higher performance, detecting 68 to 70% of groups and 70 to 73% of flashes relative to ALDIS/BLIDS.