Ordered that the order is affirmed, with costs.
The record supports the Supreme Court's determination that, after an index number was purchased by the plaintiffs (see, CPLR 306-a), the action was properly commenced by the timely filing of the summons and complaint thereunder (see, CPLR 304), and the defendant was subsequently timely served with the pleadings (see, CPLR 306-b). Hence, contrary to the defendant's contention, the plaintiffs' inadvertent endorsement of another index number from a prior proceeding between the parties on the summons in this action constituted a mere irregularity rather than a jurisdictional defect warranting dismissal of the action (see, Tufano v. Tufano, 220 A.D.2d 407; Cellular Tel. Co. v Village of Tarrytown, 209 A.D.2d 57; Chira v. Global Med. Review, 160 Misc.2d 368). Moreover, the Supreme Court properly granted the plaintiffs' motion for leave to amend the summons since the defendant was not prejudiced thereby (see, CPLR 305 [c]). Bracken, J.P., O'Brien, Goldstein and Florio, JJ., concur.