The relict and threatened butterfly Pterourus esperanza (Beutelspacher, 1975) (Papilionidae) is known to have an extremely restricted distribution in the cloud forests of the Northern Sierra of Oaxaca, Mexico. Little is known of the conservation implications of its distribution, abundance, mobility, and population structure. In total, 411 transects (from May 2010 to May 2012) were performed along an altitudinal gradient (117–3,104 m) to estimate range, population abundance, and between-year population variations of P. esperanza. Mark-release-recapture experiments were performed to estimate population structure during March and April of 2011 (N = 32 d) in a 25-km² landscape. Our results indicate that P. esperanza exhibited an extremely localized spatial distribution in the study region, mostly associated with cloud forest and pine-oak forest habitats distributed between 1,600 and 2,500 masl. Fixed transects throughout breeding populations registered a mean population density of 0.05 (±0.007 SE) individuals per 100-m transect, with no indication of significant between-year population variations (Mann-Whitney test, Z = -1.653; N = 148; P = 0.098). Based on mark-recapture data, we estimated a total population size of 243 (±36 SE) male individuals, and 43 (±13 SE) female individuals corresponding to a density of 11 individuals/km², an extremely low population density. Our results indicate that P. esperanza persists in extremely low numbers and is vulnerable to stochastic and demographic variation. Habitat protection in conjunction with explicit agreements with the local communities is required to maintain populations and ensure the continuity of important cloud forest tracts for effective long-term conservation. This research provides a case study of conservation biology of a Neotropical butterfly, emphasizing the importance of acquiring ecological data to assist management recommendations.