Data on the microhabitat parameters, especially pertaining to flow rate and substrate characteristics, of the stream-inhabiting tadpoles of the tailed frog (Ascaphus truei) were collected at two tributaries of Clearwater Creek at Mount St. Helens, Washington and at Parker Creek on Mary’s Peak, Benton County, Oregon. This is the only tadpole in North America that is highly specialized for maintaining position and feeding from algae while attached to rocks via an enlarged oral disc with many rows of labial teeth. Positions of tadpoles in the streams were correlated with oral morphology and associated anatomy. Because of the length of the larval period of Ascaphus, there are usually 2 to 3 yearly cohorts in the streams at one time. We hypothesized that the interaction of the abilities of the tadpoles to adhere to rocky substrates and the size of the tadpole would result in microhabitat segregation. Whether small or large tadpoles occupied fast versus slow water would depend on the growth pattern of the tadpole (drag) versus the changes of the adhesive abilities with size.