Ambystoma texanum (Small-mouthed Salamander) breeds primarily in temporary wetlands, and while natural history studies have suggested a minimum larval period of about 2 mo, it is not clear how hydroperiod (the length of time that a temporary wetland holds water) influences populations. I conducted a mesocosm experiment to investigate the effects of hydroperiod on the completion of metamorphosis, as well as age and size at metamorphosis. I used hydroperiods of 50, 75, and 100 d, and a non-drying treatment as a control. Survival to the end of each hydroperiod was consistent among all groups, but no individuals completed metamorphosis in the 50-d treatment. The proportion of individuals completing metamorphosis increased with longer hydroperiods, as did the age at metamorphosis. The size at metamorphosis, however, was not affected by the length of the hydroperiod. My results show that a minimum hydroperiod of 2.5 mo is necessary for populations of Small-mouthed Salamander. Maintenance of natural hydroperiods in wetlands under the threat of development is a critical consideration for the long-term persistence of Small-mouthed Salamander populations.