World almond (Prunus dulcis (Mill.) D.A. Webb) production is mostly located in areas where flowering is injured by low temperatures, and using ethephon (2-chloroethylphosphonic acid) to delay bloom is suggested as a measure to avoid frost damage. However, it is unknown if that practice could be beneficial in Mexico s warm climates. The objective of this study was to determine the effect of ethephon on almond bloom delay and yield. We evaluated foliar applications of ethephon at doses of 75, 150, and 300 mg L-1 at 10% leaf drop stage and at 150 mg L-1 during dormancy over 2 yr. In 2004, ethephon applied at 10% leaf drop stage delayed bloom by 7, 8, and 9 d at 75, 150, and 300 mg L-1, respectively (p < 0.01), and in 2005, bloom delay was 3 d at 300 mg L-1. Ethephon applied during dormancy delayed bloom 2 d in the first year, but showed no effect in the second year. Yield and fruit set were affected by ethephon applied at 10% leaf drop stage only in 2004. Neither yield nor fruit set were affected by ethephon applied during dormancy in both years. Pistil length, nut quality, harvest date, and gum exudation were not affected by ethephon. In accordance with the results, ethephon should not be recommended to delay bloom in almond orchards growing in Mexico s warm climates.