Optimizing plant density and seed size are the most important subjects of early potato production systems in mediterranean-type environments due to their effects on seed cost, plant development, yield and quality of the crop. The effects of different in-row spacing (20, 25, 30 and 35 cm) and seed size (small, medium and large) treatments on yield components and tuber yield of early potato were studied in Adana, where is situated in the east mediterranean region of Turkey, during 2006 and 2007 growing seasons. It was determined that closer spacing reduced tuber number per hill, average tuber weight, tuber yield per hill and percentages of large and medium size tubers. Total yields increased as increasing planting density up to 20 cm spacing. Planting larger seeds positively affected all growth and yield components in both years. Tuber yield per hectare was increased up to certain stem density and then started to decline at all seed sizes. However, the optimum stem density for the maximum tuber yield per hectare markedly differed depending on size of seed tubers. The optimum stem density increased with increasing seed size. Our findings indicated that size of seed tuber has further importance for growth of potato plant as well as competition aspect in early potato production in the mediterranean-type environments. Hence it was concluded that using larger tubers had an advantage for vigorous early growth and for obtain high tuber yield in early potato production in the mediterranean-type environments. Seed size should be considered during recommendation for planting density in potato production.