Basic ignorance about the ecology and life history of the endangered Mitchell's satyr butterfly, Neonympha mitchellii mitchellii, is impeding conservation efforts. To assist with recovery, we examined Mitchell's satyr butterfly population structure using mark-release-recapture techniques at two sites in southwestern Michigan in 1997 and 1998. During the single annual flight period spanning 2 to 3 wk from mid June to late July, the sex ratio changed over time, with males predominating early in the flight period and females in the latter half of the season. Scott's Method 1 and recapture decay plotting showed average residence times of 1.4 to 5.3 d. Males were more catchable than females, a probable consequence of behavioral differences between the sexes. Males were commonly found patrolling through the vegetation in search of mates, whereas females were rarely observed in undisturbed flight. Daily population estimates were obtained by the Jolly stochastic method and total brood size and flight area population densities were calculated using estimated residence rates. All population size estimates were low. Total brood size estimates ranged from 164 to 372. Peak daily flight area density ranged between 70 and 159 butterflies per ha. Adult movement was limited. Maximum range estimates were 290 m and 420 m at the two sites. Average movement distances were 37 m and 33 m. Male butterflies moved significantly greater distances than females. Remnants of a metapopulation structure are apparent, but the data are insufficient to differentiate between an extinction—recolonization structure and a source—sink structure. Butterfly movements between habitat patches within occupied sites occur, albeit rarely. Short residence times, low density and sedentary behavior make extant populations vulnerable to environmental stochasticity and human disturbance. Conservation actions need to consider the implications of these important life history traits if we are to reduce local extinction probabilities and recover Mitchell's satyr butterfly.