Silene lemmonii S. Watson (Caryophyllaceae) is a tap-rooted herbaceous perennial that grows in montane habitats throughout California and Oregon. In 1999 and 2000, I studied the pollination biology and mating system of a single S. lemmonii population occurring near Dubakella Mountain in the Trinity National Forest, CA. Although S. lemmonii is self-compatible, individual flowers are strongly protandrous and fruit set rarely resulted from autogamy in both years of the study. Silene lemmonii flowers bloom at night, yet I observed no nocturnal insects visiting flowers in 1999 and visitation by diurnal bees and flies was infrequent during both years of the study. Despite the paucity of visitors, plants exhibited relatively high fruit set (x¯  =  40% in 1999 and x¯  =  61% in 2000). In 2000, I conducted an experiment to reconcile the occurrence of relatively high fruit set with rare insect visitation. I examined the contribution of insect visitation, autogamy, and jostling-induced geitonogamy (occurring when individual flowers on the same plant brush into one another) to fruit production. I found that fruit and seed production in S. lemmonii was primarily mediated by diurnal and nocturnal insect visits, but jostling-induced geitonogamy contributed to ∼20% of fruit set. To my knowledge, this is the first study to report jostling-induced geitonogamy and the first to describe the pollination biology of S. lemmonii.