The role of nitrogen (N) as yield-limiting factor was evaluated over a 2-year period in tomato under conventional and organic management. Three N fertilization rates (0, 100, 200 kg N ha-1) and three tomato cultivars were compared under organic and conventional cropping systems. Yield response to organic system was different between the two years. In the second year marketable yield in the conventional system was significantly higher than in the organic system. Increasing nitrogen fertilization from 0 to 200 kg N ha-1 resulted in tomato yield increase and fruit quality improvement. Significant differences for nutritional quality between organically and conventionally grown tomatoes were observed. Total carotenoids concentration and antioxidant activity increased in organic tomatoes.