The cave swallow (Petrochelidon fulva) was first discovered breeding in caves and sinkholes in Texas in 1915. Within the last 50 years, it has colonized new breeding sites in western and southern Texas, and colonization has been attributed to the presence of highway culverts and bridges. We examined published observations and breeding bird survey (BBS) data, and surveyed selected culverts in western and southeastern Texas to determine the rate and extent of colonization by cave swallows. From 1957 to 1999, the breeding range of the cave swallow increased by approximately 898%, with an average annual rate of increase of 6% per year. Based on BBS data, cave swallow populations are increasing 10.8% per year, and our survey indicated that cave swallows occupied >90% of the culverts surveyed in western Texas. Range expansion is likely to continue, and additional data are needed to determine how an expanding cave swallow population might affect local barn swallow populations.