SUMMARY Sunflower is an important oilseed crop because of its wide adaptability, suitability to mechanization, low labor needs and high protein and oil contents. The present study aimed to investigate the relationship between growing degree days and yield and yield components in different sunflower hybrids and to identify environmental factors and crop characteristics that affect grain yield in sunflower without irrigation in Berlin environmental conditions. The study was conducted in the experiment fields at the Crop Science Department of the Agriculture and Horticulture Faculty of Humboldt University during 2010. The experiment was laid out in a randomized block design, with four blocks of plots of eight Turkish cultivars (Sanbro, Tarsan, DKF-2525, TR-3080, EDR- 08-01, EDR-08-02, EDR-08-03, EDR-08-04) and two German cultivars (Pegasol, NK Delfi). It was determined that the differences among all the sunflower cultivars were statistically significant for plant height, stem diameter, head diameter, 1000 seed weight, dry matter, harvest index, seed yield per plant, seed yield, leaf number, GDD (Growing Degree Daysand sun radiation. The highest mean stem diameter, harvest index and 1000 seed weight were obtained from Pegasol. NK-Delfi had the highest mean head diameter and consequently the highest seed yield (3,876.6 kg ha^-1), followed by DKF-2525 and Sanbro (3,498.7 and 3412.9 kg ha^-1, respectively). The sunflower cultivars required between 127 and 137 days, 2,263.57°C GDD and 927.54 h sunshine radiation from planting to maturity, as the mean of all the cultivars. Generally, the seed yields of the Turkish candidate genotypes were lower than those of the other sunflower cultivars. The seed yield of these genotypes can be improved with another agriculture method. The rainfall and cold weather in May slowed the growth of sunflower and also the rainfall and cold weather in August delayed maturity. The dry and hot weather in June and July created stress on plants. In terms of seed yield, NK-Delfi, DKF-2525, Sanbro, and Pegasol proved to be suitable sunflower cultivars to be grown in Berlin.