Unsuitable tillage practices have often been identified as major constraints to cereal crop production in northwest of Turkey. In an effort to increase crop production, decrease the production costs and conserve the soil from degradation through mechanical manipulation of the soil, field experiments were conducted during the two cropping periods of 2001-2002 and 2002-2003 to evaluate the effects of tillage systems on grain yield of winter wheat (Triticum aestivum L.), weed density and tillage economy on a clay-loam soil. The tillage systems used were: conventional tillage (CT) with mouldboard plough, reduced tillage with rototiller (RT) and disc (DT). The economic analysis was made by comparing the gross margin in each tillage system based on the 2004 input costs and product prices. As result of this study, weed density was significantly higher for disc and this was followed by rototiller and mouldboard plough in terms of the sum of all the weed species both in 2002 and 2003: 56, 36, 29 and 65, 52, 49 weeds m(-2), respectively. Although tillage systems had no significant influence on grain yield in 2003 but in 2002 the highest grain yield was significantly earned with rototiller, followed by mouldboard plough and disc: 4055, 3540 and 3188 kg ha(-1), respectively. Further, rototiller resulted in the highest gross margin per hectare ($ 122) significantly because of the higher grain yield compared with mouldboard plough ($ 22), followed by disc ($ 7) that provided the lowest gross margin according to the average of two years. (c) 2005 Elsevier B.V. All rights reserved.