This paper analyzes annual maximum precipitation series for the Xingu and Tapajos basins located both in the Amazon basin. The analysis has the objective of indicating a probability distribution function that can be used in design flood calculations for spillways of large dams in the region. Due to the short length of the records in the region and the robustness of the estimates of population descriptors (ex: variation and skewness coefficients) based on probability weighted moments, this approach is adopted as the main methodology.