The Coastal Tailed Frog is one of the best studied headwater amphibians in the Pacific Northwest, yet we know very little about either its seasonal movements or its distribution within and among headwater basins. During August through October 2000–2002, we studied Coastal Tailed Frogs in 81 headwater basins from managed forests in the Stillman Creek watershed in southwestern Washington State. We found a significant association between tailed frog life stage and their locations along the stream axis: older life stages were located higher in the basin than younger life stages. Data from eight streams sampled in early and late summer 2002 support the hypothesis that adult Ascaphus truei move upstream several hundred meters during the low-flow period probably after having moved downstream to breed. We also found little evidence of tailed frog reproduction in small non–fish-bearing basins, which supports the hypothesis that breeding habitat in those basins may be limiting. To test these two hypotheses, we examined A. truei occupancy in 65 non–fish-bearing headwater basins ranging in size from first to fourth order in 2003 and 2005. Occupancy increased with basin order, and we found no evidence of reproduction (eggs, larvae, or metamorphs) in first-order non–fish-bearing basins. The length of the dominant stream thread in nearly all first-order basins was shorter than the distance adult A. truei moved between early and late summer. We suggest that a headwater stream must remain watered for several hundred meters during the dry season to meet tailed frog breeding requirements. Tailed frogs probably do not reproduce in most first-order non–fish-bearing basins in the Stillman Creek watershed because those basins are too small to reliably provide habitat suitable for oviposition and rearing of their early life stages.