Orchids (Orchidaceae) are a family of flowering plants with a high proportion of threatened taxa making them an important focus of plant conservation.Orchid conservation efforts are most effective when informed by reliable demographic research. We utilized transition matrix models to examine the population dynamics and demography within sympatric populations of a species pair of terrestrial round-leaved orchids, Platanthera macrophylla and P. orbiculata. The models were parameterized from a large data set spanning 9 years from field observations of over 1,000 orchids. Life table response experiments (LTRE) were used to identify which life history transitions, and which vital rates within those transitions, most contributed to observed differences between the two species and most contributed to interannual variation within each species. Results from mean transition matrices projected finite rates of population growth that were not significantly different between the two species, with P. macrophylla near the replacement rate and P. orbiculata below