Main aims of the research were: i) to assess the degree of development of fluvial landforms on Aegean Islands and ii) to determine the influence of fluvial processes on modification of islands relief. Field studies were conducted on the Ikaria Island, with highly diversified geology and relief, typical of mountainous islands of the Aegean Sea. The island is heavily dissected by deeply incised valleys and gorges with very steep slopes. The valleys on Ikaria Island vary in size, direction, geological setting and maturity. In the four small catchments located in the northern part of the Ikaria Island four types of valleys (from 1st to 4th order, according to Strahler) were studies in detail. Uppermost parts of these valleys (1st order valleys) have slightly concave cross-sections covered with regolith without developed channels. Such forms gradually evolve into 2nd order valleys with seasonal river channels, and further downstream, into well developed deep river valleys. Ravines with channels incised into solid rock are characteristic of the 3rd order valleys. The 4th order valleys are well developed, deeply incised gorges with wide channels sometimes accompanied by river terraces. Channels of small streams, rivers and field tracks in the mountains are subject to differentiated modelling by running water. In islands of the Aegean Sea, intensity of this modelling is diversified and rather small. It depends mostly on rainfall intensity, bedrock resistance to erosion, slope inclination and aspect. Catastrophic hydrometeorological events such as one which occurred in Ikaria in October, 2010, are responsible for rapid modification of whole valley floors and modification of river channels at lower river runs, within deltas and alluvial fans.