During the rainy season of 1998, a field experiment was established in Cocula, Guerrero (hot subhumid climate, Awo) and in Montecillo, México (semiarid climate, BS1), to evaluate the effect of nitrogen (0, 10 and 20 g m-2) and environment on phenology, yield and its components, water use efficiency (WUE), and crop evapotranspiration (ETc) and heat units (HU) accumulated during the growth cycle of sunflower (Helianthus annuus L.) cv. Victoria. The crop was planted on June 1 at a density of 7.5 pl m-2 in both climates. In Cocula, maximum and minimum temperatures were more extreme and rainfall was more intense, while soil was poor in total nitrogen, compared with Montecillo. Crop growth, yield and its components, and water use efficiency were affected significantly by the environment, nitrogen and the interaction environ ment * nitrogen. The crop cycle in the hot environment was 36 days shorter, with a greater accumulation of HU and ETc. Yield and its components and water use efficiency were significantly higher in Cocula. Nitrogen positively affected the evaluated variables. The interactive effect of environment * nitrogen was observed clearly, since in Cocula there was response to the application of nitrogen in most of the variables evaluated, while in Montecillo there was not.