Climatologic and basin characteristics affecting the annual runoff in Finland are selected by the orthogonal regression method. Climatologic variables, especially seasonal precipitation and mean annual temperature, are found to be much more important than basin characteristics such as soil type and vegetation. Frost depth is inversely related to annual runoff. The percentages of cultivated land and peat land are not significant variables in these data. The simple linear multiple regression approach was successful (R = 0.943, s0 = 34 mm) in developing a reliable prediction equation. However, no statistical procedure can uncover the underlying laws governing runoff until the basic physical relationships are better understood. Furthermore, most available climatologic and basin characteristics are only indices of the combined effects of several physical factors. Hence, the utility of some of the more complex statistical approaches is questioned.