The upward trend in the number of Legionnaires' disease cases that began in 2017 continued in 2018 (+31%), with 2,133 cases, representing a notification rate in mainland France of 3.2 per 100,000 inhabitants. Analysis of the characteristics of cases occurring in 2018 shows results comparable to those of previous years. The increase in 2018 is mainly due to the resurgence of sporadic cases observed in June, which accounted for 21% of cases. One hypothesis to explain this increase is the influence of meteorological factors (temperature, precipitation, and humidity) on the occurrence of Legionnaires' disease cases. In addition to the multifactorial study including meteorological factors conducted by Santé publique France on cases from 2008–2015, similar analyses of data from 2008–2018 are currently underway to document the influence of meteorological factors on the increase observed in 2018. Although no outbreak (more than 10 cases) was identified in 2018, it is important to investigate all suspected clusters of cases methodically and without delay in order to limit the number of cases and identify any potential source of contamination. It is therefore essential to maintain the responsiveness of all local partners and to continue promoting the systematic collection of respiratory samples, which allow, on the one hand, the identification via PCR of Legionnaires’ disease cases not detected by urinary antigen tests (which are more specific for Legionella pneumophila serogroup 1) and, on the other hand, to obtain clinical strains that enable the documentation of clustered cases and, through comparison with environmental strains, to identify probable sources of contamination.