The natural drainage network in a region is analyzed in order to investigate scaling properties and the form of the probability distribution for basin areas along a coastal boundary. The Horton/Strahler approach used in the classical description of the drainage network within a single basin is extended to a series of independent though conterminous basins with outlet to the sea, assuming that a regional area ratio RA, analogous to the Hortonian area ratio, holds for independent basins. A multiplicative factor Rc is also defined as the average ratio between the number of independent basins of a given order &ohgr; and those of order &ohgr;+1. The cumulative area distribution (CAD) for drainage basins that drain along the coastal boundary is obtained as a power law in the form Pa>∝a-&ggr;, with &ggr;=log Rc/log RA. The derived form and parameters of the CAD are shown to hold for the Liguria region of Italy (≃5700 km2 in the northern Mediterranean) as well as for the whole continental Italy (≃250,000 km2). The fractal dimension of the regional system encompassing all drainage areas of basins with outlet to the sea is derived in the form D=1/&ggr;. The analytical results obtained are shown to agree with the theoretical expressions already available in the literature for optimal channel networks. ¿ 2001 American Geophysical Union