The sex pheromone of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae), from the Niagara Peninsula, Ontario, was investigated using chemical analysis, GC–EAD, and field trapping experiments. The pheromone gland contained: (Z)-11-tetradecenyl acetate (Z11-14:Ac), (E)-11-tetradecenyl acetate (E11-14:Ac), (Z)-11-tetradecen-1-ol (Z11-14:OH), and (Z)-11-tetradecenal (Z11-14:Al). The average amounts of Z11-14:Ac, E11-14:Ac, Z11-14:OH, andZ11-14:Al were 40.40, 0.83, 0.47, and 0.13 ng/female, respectively. Eight other structurally related compounds, (E)-11-tetradecenal (E11-14:Al), (E)-11-tetradecen-1-ol (E11-14:OH), pentadecan-2-one (15-2kt), hexadecanal (16:Al), hexadecan-1-ol (16:OH), heptadecan-2-one (17-2kt), octadecanal (18:Al), and octadecyl acetate (18:Ac), were also identified. In a field trapping experiment, adding Z11-14:Al to lures containing a 100:3:5 blend of Z11-14:Ac, E11-14:Ac, and Z11-14:OH in an amount equal to 2% of the main component significantly increased the number of moths captured in apple, Malus domestica (Borkh.) (Rosaceae), orchards. The removal of Z11-14:Al from lures containing a 100:2:1.5:1 blend of Z11-14:Ac, E11-14:Ac, Z11-14:OH, and Z11-14:Al resulted in a > 50% reduction in the average total number of moths captured in a trap. This study provides the first evidence that Z11-14:Al is present in the pheromone of an eastern North American population of C. rosaceana.