In the face of climate change-induced economic uncertainties, households may em-ploy migration as an adaptation strategy to diversify their livelihood portfolio through remit-tances. However, it is unclear whether such climate-related migration will be documented or undocumented. In this study we combined detailed migration histories with daily temperature and precipitation information from 214 weather stations to investigate whether climate change more strongly impacted undocumented or documented migrations from 68 rural Mexican mu-nicipalities to the U.S. from 1986−1999. We employed two measures of climate change, the warm spell duration index (WSDI) and precipitation during extremely wet days (R99PTOT). Results from multi-level event-history models demonstrated that climate-related international migration from rural Mexico was predominantly undocumented. We conclude that programs to facilitate climate change adaptations in rural Mexico may be more effective in reducing undo-cumented border crossings than increasing border fortification.