This research was conducted in order to determine effects of irrigation based on different moisture levels of growing medium on yield, fruit quality and water use efficiency of soilless grown greenhouse tomatoes during fall and spring seasons of 2010 and 2011 in PE covered greenhouse. The treatments were composed of full and two deficit irrigation programs. Irrigations were started automatically according to the soil moisture sensor readings when available moisture capacity of substrate was consumed 20% (full), 40% (deficit 1) or 60% (deficit 2) respectively in the plant root zone. Experiments were set according to the randomized blocks design with four replicates. Drip irrigation method was used in nutrient solution supply and timing was based on soil moisture sensors placed at root zone. The duration of irrigation was set according to the daily leaching fraction which was kept around 30-40%. In both seasons the highest total and marketable yield was obtained from plants under full irrigation. Compared with full irrigation, total yield in autumn decreased 19.2 and 19.3% in deficit 1 and deficit 2, respectively, while it was 35.2 and 32.1% lower in spring. It was determined that plant growth, water use efficiency (WUE) and some fruit quality parameters showed differences in irrigation treatments according to growing seasons. Total soluble solids, titratable acidity, EC of fruit juice, total antioxidants and vitamin C increased with water deficit. The highest WUE was determined in deficit 2 in autumn and full irrigation in spring. It was concluded that water deficit could be applied in autumn, however, more attention should be paid to irrigation since there are more risks in spring season production.