ABSTRACTUp till now studies of basin parameters influencing runoff in West Africa have largely been confined to very small basins. For this study of 10 medium sized basins in Southeastern Nigeria, principal components analysis reduced 14 runoff, rainfall and physiographic indices to five orthogonal components, viz basin size, landuse, basin steepness, channel steepness, basin altitude, which together explain 88.4 percent of observed variance.Five component variables, viz basin area, percentage of basin area covered by forests, drainage density, dry season rainfall and channel slope are used in a regression which provides a prediction of annual runoff, with a coefficient of determination of 0.72.Explanations are suggested for the significance of these variables for runoff.