<p><i>Pseudochazara williamsi</i> ranks among the most threatened butterfly species in Europe and globally is currently listed as Critically Endangered in the 2025 Red List of European Butterflies. In study we analyze the status of the species through the compilation and validation of historical records, as well as field surveys conducted between 2023 and 2025. Endemic to the high mountain ranges of the southeastern Iberian Peninsula, the species has experienced documented extinctions of several local populations, accompanied by a pronounced decline in overall abundance. Moreover, its altitudinal distribution has undergone a substantial contraction, with the mean elevation of occupied sites shifting upward by 217&#xa0;m when comparing data gathered during the present century with historical records from the last century. Marked changes in phenology have also been detected, most notably a shortening of the flight period driven by a contraction at the end of the season and a slight delay in its onset. In parallel, the species’ potential distribution area has declined dramatically, with an estimated reduction of 92.05%. Collectively these results reveal a highly alarming conservation scenario. In response, we propose a suite of management recommendations, developed in close collaboration with regional environmental authorities and stakeholders, aimed at halting the ongoing decline of <i>P. williamsi</i> populations. Climate change currently represents the principal threat to the species, with its impacts further amplified by interacting pressures, including livestock management practices, the abandonment of traditional mountain activities in southeastern Iberia mountains landscapes, and the widespread presence of environmental pollutants, among other factors.</p>